The problem is not American Sniper persay. The problem is lack of proper critiques of the war like Apocalypse Now.
I’m not on the the left, you don't have to be on the left to realise that the war was mistake. It is not really about the soldiers, it is about the failed policy.
There is still a denial of the catastrophe of the Iraq war in the US. But strangely more people are willing to discuss Iraq as a mistake than Vietnam. That is a strange one.
Vietnam was so obviously a mistake, it had even less legitimacy than Iraq. What's more the Vietnamese get on better with the Americans then they do the Chinese, but obviously there has been years of distrust.
I think comes down to conflating the veterans, with policy. They are two different thing and should not be confused.
Vietnam, taught the US that money and resources still doesn't beat asymmetric/guerilla warfare, but they haven't actually learnt that lesson yet.
Ironically ISIS are trying to be a state so they can be beaten in a sense, as they are fighting conventional warfare and less asymmetric. But you can't beat whatever comes after by military power alone.