Is the idea that if the Syrian government commits atrocities then Western powers have to intervene in the war? So to prevent a probably-disastrous intervention people need to deny that the Syrian government commits atrocities? I don't think that is a logical chain of reasoning, if that is indeed what is going on. There are all sorts of horrors in the world where additional intervention by outside powers is likely to be worse than inaction. It doesn't mean that we should pretend that the horrors don't exist.