Why are Machine Guns legal? What does anyone need with one?

We don't have needs in this country, we have rights.

No one needs cars that do 3X the speed limit. No one needs booze. No one needs a lot of things. So really, I have no need to answer your question, because it's a snoopy, intrusive question. I want them, so I have them, and it's none of your business. However:

A semi-automatic is not a "machine gun," which is by definition full auto. So you actually don't know enough about what you're asking to phrase a clear question.

Full autos have been all but eliminated. There are less than 200K in existence, no new ones are allowed since 1986, and they cost $5000 and up, some in the hundreds of thousands. Nor has a legal full auto EVER been used for murder since the National Firearms Act taxed and restricted them. (There are two exceptions. Both were POLICE engaged in the drug trade.)

Illegal ones get smuggled in or made in labs, just as drugs do. Banning cocaine hasn't stopped anyone from acquiring it, it's only created turf wars and circumstances where addicts are afraid to ask for help.

The 2nd Amendment is not to protect hunting. It is to protect the right to make war against invaders or despots. In fact, you'll find in the Constitution a reference to "Letters of Marque and Reprisal." This acknowledged that private warships with cannon were common enough to provide laws for. Private artillery was common through the Civil War.

Finally for now, at 600 rounds per minute or more, machine guns are insanely expensive to shoot. I spend about $100 per shooting minute on ammo for mine.

Citizens don't need machine guns, they want them. They think the 2nd amendment means all arms. Some people would cruise around in tanks if they could.

Machine guns and semi-automatic rifles are different.

Machine guns are good for 2 things. Wasting ammo and suppressing fire. You can kill more things out in the open with controlled pairs than with a hail of bullets shot into the air.

Machine guns (fully automatic weapons which are weapons that keep firing rounds as long as the trigger is depressed) are not legal. Many uninformed people make this mistake. A rifle that is semi-automatic (will fire one round every time you depress the trigger) is legal; in the military that same rifle has another option on the selector switch (at least when I served) which takes it from semi-automatic to fully automatic. Civilian weapons have no such ability unless someone has done some alteration to that weapon to make it fully automatic. This is the type of misinformation many anti-gunners spread falsely (not referring to you, Ma'am), just as the misnomer "assault rifle" is used by people who know no better or do know but spread it anyway. There is no such thing as an "assault rifle." Any weapon can be used to "assault" someone. If you take a shotgun and attack someone with it, then it could be called an "assault rifle." But the anti-gun group use the term to describe AR-15s (the civilian equivalent of the M-16, without the fully automatic capability), an SKS, AK-47 or any number of weapons that were originally made for combat action. Most people who own AR-15 (the most popular of the semi-automatic carbines or rifles on the market today) use it for recreational shooting, hunting and home defense. Why would you need a semi-automatic rifle for home defense? For the same reason our Forefathers put the 2nd Amendment in the Constitution. Americans should always be able to keep their Country from becoming a police state or a dictatorship. And no, I don't own one. Hope this helps.

Let's go with the Obvious first: Because I can. It's a Constitutionally protected right. And Yes, while they are legal, they are HIGHLY regulated and incredibly expensive.
Second, I don't think you understand the meaning of the term "Machine Gun". It is typically used to describe a weapon that can fire multiple rounds with the single pull of the trigger, however, this is also covered by the term "automatic weapon", which refers to the same thing. So "Machine Guns" is used to describe a larger weapon than a standard rifle that is often belt fed and sometimes called a 'crew served weapon". I can honestly tell you that there has not been a murder in the United States with a Crew served weapon, EVER. Despite what Hollywood wants you to believe.
So let's boil it down to what I think you're getting at and that is select-fire NFA (National Firearms Act) controlled weapons. This is your typical rifle that can be made to fire more than one round with the single pull of the trigger. Now we're getting into the dangerous stuff, those things carried by all the gangs and used in all those drive-by shootings you mentioned. Except, not. Last year there were 0 (that's zero) murders with a select fire weapon.
As a matter of fact, there were more murders with hands and feet than with ALL rifles combined (to include the evil ones)! Knifes killed more people than rifles, pools killed more people than rifles, texting killed more people than rifles, etc...
So to answer your question, I can have one because the Constitution protects the rights of Americans to lawfully possess firearms for the express purpose of defending oneself from anything up to and including (especially) a tyrannical government. Now some say that the people are outgunned and can't match the might of the Military if it were ever turned on us, but just look at what bunch of guys in the Middle East were able to do.

I think that honestly I would love to own an old style "machine gun" say from WWI or WWII just for the oddity of owning it.
I think though that most of the drive by shootings or criminal activity involving assault rifles that can shoot full automatic are not legally obtained and that more effort needs to go into getting those weapons off the street. I would say that almost every legal gun owner is very responsible with their guns and keeps them as secure as possible.
Yes you do see the occasional dumb ass who leaves a loaded gun without a trigger lock on the nightstand and some 2 year old kid plays with it, or the parents who fail to secure their weapons and their teenage kids gets pissed off and decides to settle a score.
Until our elected leaders decide to go after the criminals and punish them according to the law then your never going to see automatic weapons off the street.

Sgt Kelli Mays The laws on the books keep any legally owned machine gun for the most part out of the hands of any criminals. They are super expensive (Cheap ones are around $10,000) there are tax stamps and background checks that are much more in depth that buying a handgun. Since 1986 there are not allowed to be any more machine guns manufactured for sale to the civilian population. The ones that are out there now are used and being traded. They will eventually go the way of the dodo bird and you will only hear stories of them.

I do love when people that don't understand the Second Amendment claim that they support it. The 2nd does not give you the right to hunt or to even protect yourself with a firearm. There is no guarantee for any of those things in the Bill of Rights. You have been given the right to own a firearm for one reason only. To be able to stand up to the government as a group and overthrow it if need be.

When this was written there were no planes and tanks. It was men with guns facing each other and firing single shots. Most of the guns were civilian manufactured. It was fair for both sides and if enough people did not like the way it was going they could of marched to the Capital with guns in their hands and ended the reign of the person in power. That is why you are allowed to own a gun.

Now modern times there are force multipliers. Machine guns being the least of them. Planes, missiles, and bombs have made it nearly impossible to defeat a government with just guns, but we still have that option. Would everybody being able to own a machine gun make a difference in the power of the people? I don't believe so. For that reason alone I have no problem saying that not everybody should have a machine gun.

The only correct statement you made was that you didn't know much about guns. Automatic weapons are very strictly regulated by the ATF and have been for 80 years. Autoloading rifles are the most efficient way to protect yourself (that's why the military uses them), and depending on the caliber and size of game are perfectly suited for hunting. I hate to break it to you (no I don't), but no situation the requires the use of a firearm is completely safe. If you were safe from a person trying to kill you, you wouldn't need a gun. That being said, you are never completely safe. Wear a seatbelt, wear a gun, keep fire extinguishers ready, and be prepared for whatever emergency may rear its head.

Like most things with high emotional content, the arguments are low on facts and high on hysteria. Let's start with some definitions:
Machine gun: A weapon which fires more than one bullet per trigger squeeze. Also known as "Full Automatic." These weapons are already illegal, with some very limited loopholes, like having a Class III Federal Firearms License (that is the license required to run a gun store.)
Semi-Automatic: A weapon which fires ONLY ONE bullet per trigger squeeze. Nearly all legal guns (except bolt actions and really old guns) are in this category.
Bolt Action. After firing a single bullet, you have to work a bolt, or pull down a lever or otherwise take some action to get the weapon ready to fire the next round.
Need: Used politically, it means that I have the right to determine what you are allowed to have, and I can disparage your desire to have something that I don't think you "need." Do you need to have a car? Do you need a dryer? (Isn't hanging clothes on the line outside, and saving all that energy good enough or you?)

Ownership of a machine gun is something I will not defend. Pulling the trigger on a weapon means you have accepted the complete responsibility for where the bullets go. if you kill a burglar, but the bullet passes through his body and kills some innocent 1/2 a mile away, you are guilty of murder. Even professionals can't be that accurate with multiple bullets coming out of the barrel.

Some survivalist types will say that when the mob comes for them, they will mow them down. Unlikely, as well as slightly hysterical. With a machine gun, even in the best situation, only about 1 bullet in 3 kills the target, The rest miss, or do additional damage to a corpse that hasn't hit the ground yet. I have a .45 automatic (That's a pistol that only fires one round per trigger squeeze.) If a mob of 20 comes to kill me, they can do it, but I'll kill 7 of them first, and that's enough, in my opinion. Besides, if I kill a few, the rest may decide to look for someone who isn't armed.

Me personally, I'd gladly surrender the right to machine guns, weapons over .50 calibre (1/2 inch in diameter, but excepting black powder weapons which can be much larger and have no record I can find of being used in crimes in this century), explosives, poison weapons, and similar things, if we could once and for all quit having to defend my right to self-defense, sport, and hunting, year after year. But certain people like Obama and Monica Lewinsky's ex-boyfriend's wife have stated that they will keep coming until they disarm our society. I take them at their word, and I'm not giving an inch without some recognition that I have rights too.

So what's bad about that? Australia recently used their registration database to force their citizens to turn in 604,000 personally owned weapons which were then destroyed. A police chief from one of their cities recently reported that EVERY category of violent crime has increased since then, including a 300% increase in assaults on the elderly in their homes.

Do we have a numerically high homicide rate in America? Yes. Are the the third most populous nation on the planet? Yes. Could that be the reason for the high number? (Queue Jeopardy music.)

In fact, our per capita homicide rate is lower than many European nations with high gun control laws.

What is my solution? First, we need to ask if guns are the problem or if something in our society is the problem. Are people frustrated and desperate because they cannot find work? Yes. Are the mentally ill undercared for? Probably. Are people frustrated because their government doesn't listen to them? Sure. Are people worried about having to eat dog food when they retire? Damn straight! Are people concerned about the every increasing tax bite? Yes. Are people concerned about the way the government overspends the budget, putting the nation into unpayable debt? Yes. What is the number 2 illegal import into the US (behind illegal drugs)? Guns, often fully automatics and sawed off weapons, both of which are already illegal. Just how many mass murders in the last 3 years would be prevented if we had complete background checks? Only ONE, the Virginia Tech shooting, and it wouldn't have happened if Obama hadn't blocked a bipartisan bill restricting gun ownership to the mentally ill. What two cities have very restrictive gun control laws, yet constantly are number 1 and 2 as the Murder Capitol of the United States? Washington D.C. and Chicago. And if gun control is such a good idea, why is the record so poor in Washington D.C. and Chicago? ........ No matter how much thinking you do, my answer is that it obviously shows that it isn't a good idea.

We have a lot of problems to solve in this country and we need reasoned discussion about them, rather than playing politics for political gain.