> There's a false equivalency here: Only one side is barrel bombing people indiscriminately, torturing people by the tens of thousands, and systematically exterminating an entire group of people.

That seems blatantly false to me. The Assad regime is certainly guilty of all the things on your list, but ISIS are also murdering and torturing people by the tens of thousands and systematically exterminating entire groups of people (has everyone already forgotten about the Yazidis, if nothing else?). Insofar as differences in scale exist, they seem to exist only because ISIS doesn't have the capacity to kill as many people as they'd like. Both groups have institutionalized horrific violence as a matter of policy.

Syrian civil war has much more than just these two actors.

That's absolutely true, I merely mentioned the most obvious counterexample in terms of deliberate atrocities. Most of the other actors are also guilty of deliberate human rights violations on a fairly massive scale, but I thought my simple counterpoint was quite sufficient to rebut the parent.

Precisely. ISIS is actually far less of a factor in the overall shape of Syria than they are in Iraq.

You won't find me defending the crimes of the Syrian government. (Or of anyone else in the war!) But I think that there's a danger of letting your perfectly justified moral outrage distort your ability to predict. I do not think that the Syrian government will be as isolated as North Korea after the war. It's not as isolated as North Korea now and outrage will fade further after the war. I predict that there will be less diplomatic pressure on the government after the war. The EU and neighboring states will be more interested in stopping/reversing refugee flows than in punishing the Syrian government for wartime atrocities. Any stability will be considered good stability.

I predict that Assad, like most heads of state, will never be held accountable for his government's crimes. I do not even see how an outside force could bring him to justice without subjecting the Syrian people to even more misery.