There's only one thing that's certain:

none of it is as simple as most people want to pretend it is.

It's not JUST because Muslims kill each other, it's not JUST that Syria has been interfered with by a bunch of other countries, it's not JUST that Putin has been playing both sides, while mostly helping Assad, and it's especially not as simple as "telling the refugees to go home."

Get as self-righteous as you want, you'll be ignoring at least half of the factors and problems, and doing the equivalent of squeezing a balloon in the middle,and expecting the ends not to bulge.