Also, Turkey is relaxed about ISIS because it wants rid of Assad. President Erdogan had an almighty falling-out with him a few years ago. Unfortunately, as with other examples of long-running rivalries in the region, these squabbles have all developed sectarian character (in many cases, not because the squabbles are fundamentally religious, but because religious identity politics are an easy way of mobilising support for causes that might not otherwise bother the populace). Once unleashed, these sectarian/identity disputes aren't going to be fixed by negotiation due to the rabid hostility that results. The US has already accepted that NATO contains a Muslim Brotherhood-leaning Islamist government... yes, Erdogan hates al-Sisi as well... It's a screwed-up web of intrigue that I would much prefer we abandon to its fate. But we can't!
Beware identity politics.... I hope it's not going to keep growing in the UK...