Is heavy armor outdated on the modern battlefield?

Heavy armor will never be obsolete. I love the Stryker, but wouldn't expect it to defeat the sheer numbers of T-80's, etc that can be thrown at them. The psychological effect they have is a huge multiplier as well.

No, especially when you need to control territory. If we had even a few dozen M1A2 in Ukraine or near, Russia would not have the attitude they have now with Crimea and Ukraine.

Just because our last fight was COIN does not mean the next one will be.
We need heavy armor in Europe, Baltic states and Ukraine NOW.

Your enemy always gets to choose the type of war you will fight. Tanks are outdated now simply because no one else has the capacity to fight them. As soon as the tanks are gone, there will be a immediate and urgent need for them.

We never fight the last war because we train for that war, we always fight the war we are not training for.

The reason we fought an insurgency in Iraq was because they were so easily defeated in the conventional invasion. It took them a while to figure out what worked and IEDs became prominent. Simply because they were effective. While an MRAP is a great tool for IED's it is near worthless in a conventional attack.
If we were to limit our conventional forces or scrap the tanks our enemies simply would adjust back to the conventional fight.

I do think an M551 Sheridan or modern version would have been very useful in Afghanistan.

They will become obsolete when a man portable anti-armor weapon becomes a feasibility, like the laser death ray in the movie Congo.

I think those that say heavy armor is obsolete suffer from tunnel vision. They're basing their opinion solely upon the current conflicts. A tank is designed to rapidly seize territory and engage the enemy at stand-off range. They employ speed, shock, and tempo to their advantage to accomplish this. Urban environments significantly reduce the inherent advantages that armor brings to the table. COIN campaigns do as well, since restrained force is not a strong point of tanks either. Heavy Armor is admittedly not well suited to our current OEF campaign, nor was it particularly useful once Iraq transitioned to a counter-insurgency war.

However, basing our tactics and force structure upon the previous war has continued to be disastrous for the U.S. military. While an armor-centric force may not be the future, it is a capability we need to maintain. It's not unlike the vertical envelopment capabilities that airborne troops offer. They're not terribly useful in a COIN campaign either, but that doesn't mean we should drop the capability altogether. Nobody wants another Task Force Smith, where our unpreparedness and lack of equipment resulted in disaster.

I'm horribly biased, but NEVER! The problem is that we stare too long at one kind of war and forget that there are others. Sure, the Abrams had limited utility in heavily populated Iraqi cities or the mountains of Afghanistan, but it has an important place in maintaining a decisive weapon against forces that will have to fight you in the open across large swathes of land. Not every enemy will be a tribal hiding in a cave or village. Even then, Marine tanks in the Stan were stunningly effective when they could be brought to bear...that asshole hiding in a wadi 700m away taking potshots at you suddenly found himself a lot more visible and a lot less safe.

Part of the issue with continuing production is that once theproduction line goes cold, it is next to impossible to restart it again. So is it better to keep the line open, churning out small numbers of tanks than to shut it down in the hopes that we won't need to produce more?

No, Heavy Armor is not outdated and If you have never watched the History Channel the Greatest Tank Battles, you have to see the Battle known as 73 Easting, Gulf War 1991. Tanks against Tanks are why we still have Tanks. Russia won't stop using tanks so, Mount up!

No it is not!

I think it does still have a place. Desert Storm is a great example.