I think the most accurate representation of the problem is The Onion's. I've no confidence that us going in (not matter how far) will do anything but make matters worse. The world is a very complex place, and sometimes we just can't fix things. Still, not trying seems just as bad. In a better alternate universe we could get a coalition together to go in, arrest Bashar, have an actual trial with evidence and find out "what really happened".
In our existing world the options seem to be: kill people and blow things up or let Bashar (and/or his loyalists) kill other people and blow other things up...in either case rebel forces will kill people and blow things up, though I suppose we could help them do that more effectively as well.