Why can't we grow beards?

Unfortunately uniform standards are being relaxed in a number of uniformed professions( Police, Security, Fire) and beards are being allowed further eroding uniform standards, this is a mistake as its difficult to maintain the standards associated with a "well groomed beard" in addition uniformed professionalism and image will be negatively impacted, the beard issue was discussed at my organization over the years and the "no beard standard" was maintained as controlling a "beard grooming standard" is a challenge and you will have some guys running around looking like Santa Claus!! In my opinion beards should not be allowed in the US military ( excluding spec ops) uniformed professionalism and image should be maintained.

One reason: Gas masks

Well let's see. I have been out for a while, but I believe if you go get a Ranger tab and some Airborne wings and a nice cushy special operations billet, they will probably send you over to the desert and let you grow a beard. /tongue removed from cheek.

Why would anyone want to wear a beard, you might it makes you feel cool, kind of macho, but in the event you need to put on a gas mask then your SOL, I wear one now but I'm not in the Army but a proud military veteran

You need to distinguish between what the Army allows and what the Army is TOLD they will allow. While many of the things you listed do, in fact, occur, that does not mean that the Army has a policy of condoning them, quite the opposite. There is also a distinct difference between "looking professional" and being professional.

Just an FYI...using a gas mask with a beard is a recipe for failure.

SP4 Byron Skinner…Well your obviously not in the SEALS or Special Operations. In many Infantry Companies or Cavalry Troops Mustaches and small beards are not seen by officers. With the hooded chemical protection mask the gas mask story became a joke. Funnier yet Gas Masks and mess kits usually ended up in the same place any way. Tattoos had always become a matter of unit policy at the Battalion level. Has any body seem MSMC General James Mattis right arm???

Regulations will tell you it’s because of the seal on your protective mask. But as you have already stated, that’s really not the issue.

Bottom line, it’s not liked. Until someone in position to change the regulations is there advocating for beards, it’s not a subject officers are going to discuss. It’s clearly not about looking professional as we have numerous service members of all ethnicities getting shaving profiles, waivers and religious exemptions. So it just comes down to it not being liked at the highest levels.

First thing that comes to mind is the protective mask issue. I worked in a nuclear power plant for a year and they were allowed to have beards but had to slick them down with Vaseline so thee half face and full face masks would seal properly. Second is that the Dutch Army had beards in 1983 and they looked like poor lost hippies. Third is that clean shaven is an easy standard to manage, just like the venerable high and tight

The main reason for the beard regulation is that it is difficult or impossible to seal a protective mask when sporting a beard. VX, GB & GD nerve agents would ruin your day. The beard can interfere with the seal of the mask.

With this attitude don't expect to move up the promotion ladder any time soon.
I cannot comment on the tattoo sit. in the Army these days, but I can assure you that the criminal history and substance abuse problems are miniscule compared to the mid to late 70's. I know first hand of one event where the entire bridge and engine room watch was stoned to the gills in the middle of the Indian Ocean. I'm talking from the messenger of the watch to the officers in charge. In those days it wasn't 'cool' to serve, and the military had to make use of what they could get.
As far as beards in the Navy went, you simply had to file a request chit to grow a beard. You were given 30 days to prove you could grow a decent beard. No scraggly or patchy beards allowed. As a precaution for NBC warfare I kept a large jar of Vaseline in my gas mask bag. When they called for a mask, it only took a second to slather my beard to ensure the mask sealed properly. I do, however know of two separate incidents where sailors got their beards caught in machinery and suffered severe injuries as a result (even though we kept our beards facial conforming ie - short). Aside from that, beards for soldiers would seem to me to be a bad idea for the following reasons (in general). Hand to hand fighting - even a short beard can make a wonderful 'handle' for your opponent. Field hygiene - beards make a great perspiration and 'critter' trap, not to mention some of the messier MRE bits and pieces.
Then there's the issue of dealing with the grooming standards of the more "sensitive" types who seem to think the regs aren't for them. NCO's have more important things to do than to be 'shaving police'.
Lastly we come to professionalism. All countries have exemplary military professionals to some degree or another. Few have a higher percentage of members in that category than the United States. The ones that do are usually smaller countries with long histories of martial excellence. The Gurkhas are one example that comes to mind readily. I don't see where the presence or absence of a beard has any effect on professionalism. That's a state of mind that affects behavior more than appearance. As a Corporal, you're just beginning your military career. I hardly think you're an expert on professionalism yet. I'm not slamming you, I'm making an observation. At the age of 62 I look back at many of my 'oh-so-certain-I'm-right' beliefs and I realize just how far off base I was.