The facts don't really matter, dick. The problem is you are trying to analise rationally a completely irrational and confused situation. Nobody really knows who is fighting whom, who the"good guys" are and who the "bad guys" are.
The UK government is complicit in this. A couple of years or so ago it was eager to support "rebels" in their overthrow of the Syrian government. It did this, as usual, without having much of a clue what was going, who was who or what would happen after "victory" had been secured. It was swept along on the tide of the ludicrously named "Arab Spring". And we all know how well that turned out.
Now it has sent aircraft to bomb the rebels it was thinking of supporting just a couple of years ago. No doubt when that's been going on for a few months they'll discover that was less than wise. You simply could not make it up and with such abject incompetence western governments would do well to steer clear of the whole shooting match. Let them slay each other to their hearts' content.
To paraphrase the excellent Mark Twain "Best to do nothing and let people think you are foolish rather than do something and remove all doubt".