Liberty says that it's wrong to speculate that the reason America hasn't intervened yet is because it (America) doesn't want to make the situation worse.
This seems a bizarre criticism to me. Firstly, because the article doesn't particularly argue this anyway.
But secondly, isn't that actually entirely plausible? As Liberty him/herself recognises, America knows an intervention could provoke a further degeneration into sectarian chaos in which it would get bogged down, and desperately wants to avoid this. Isn't that America holding back from an intervention because it doesn't want to make things worse? You don't have to impute any sincere democratic motive to the US ruling class to speculate that it would rather not intervene because such an intervention would (from the point of view of its own interests) make things worse.
The article does not give America any "cover" for anything, so the bland anti-imperialist truism about America's project having "nothing to do with democracy or peace but everything [to do] with America controlling this strategic area of the world" is, I'm afraid, wasted.
Liberty seems to agree with the central thrust of this article, which is quite clear: it is the policy of the Syrian ruling class, and not the American, that is the "main enemy" in Syria right now, and that the "imperialist intervention" of Russia, Iran, and China to support Assad is a more pressing and ongoing problem than a potential military intervention from the USA.
Those are the fundamentals of the AWL policy, with which Liberty appears to agree. I don't really understand the quibble.