The case for intervention seems strong in humanitarian terms and as a matter of realpolitik (not that rare a confluence). But the case for intervention looks weak in terms of ability to actually get it done right. Starting at the top, the president, while not at all dumb, is not some reincarnation of Bismarck. The number two (Kerry) looks like an even shakier proposition than the President. As does the NSA. The various military chiefs and intelligence chiefs may be capable enough in some narrow sense, but their record in Iraq and Afghanistan suggests that they (or the institutional culture they are embedded in) cannot (or will not) do more than their "own job", which is too narrowly defined to make them the likely agents of a brilliant strategic coup here. And the broader culture is just not interested in the role of imperialist OR worldcop. Liberals who want humanitarian intervention would prefer that it be bloodless. Right wingers who want to kill them all and let Allah sort them out have no idea what they are up against in detail and what that business of killing them all may involve at home and abroad in terms of costs to THEMSELVES.
Not only does the US lack credibility about its intentions or information, it lacks credibility about its ability to get things done right. That may be harder to fix, especially if the perception is partly correct.
Of course it's possible that they have a brilliant plan outline and are working to fill in the details (not just in terms of military planning, but PR management, international partners etc) and given a little more time, will get it right; but really, who do you think HAS that great plan?(I woudlnt know about it if they did, but how many people here think Kerry, Rice, Hagel whatever actually have a brilliant strategic plan in their head and are feverishly laying the foundations for getting it right as we speak?)...and of course its possible that they dont even need the time; that they jumped in with all this red line, got-to-take-action stuff because they ALREADY had the foundations laid in secret and will soon show everyone how wrong the doubters were..well, how likely does that seem to anyone here?
Pessimism may not be that irrational.