At that time, I saw a report by the Australian government that looked into the matter and came to the blunt conclusion that the major conflict was a useless conflict from the West view and should not be seen as a war between goodies and baddies but between baddies and they wanted no part of it.
This might be true.
If it is true, then I'd like to know which air force - which given what you say certainly wouldn't have been the RAAF - was flying Hercules aircraft on biscuit bombing runs onto the PKK/YPG/HPS on the top of Mt Sinjar.
Apparently 60% of the "humanitarian aid" landed either went *bang* or was loaded into things that went *bang*.
And all those small sized carbines ? Definitely not specifically bought in the Balkans so the HPS had weapons suitable for girls who really didn't want to be sex slaves who might have needed to fight their way off said mountain.
Word is they were all even given back afterwards, as Qandil had made it clear this was a one-shot operation by a group who definitely wasn't recruiting child soldiers any more, in the same way Western countries weren't arming child soldiers.
Now, going to the specifics.
Various PKK-aligned groups were the ones actually shooting at ISIS with some success in 2014. If you back the Turks, then you are going to need to get them to not be holding the passes against ISIS in Qandil, on the road to Erbil, in Sinjar and so on. Also note a decent chunk of Kurds are pro-ISIS. As are a fair chunk of Turks.
No one cares about the brutality of the Shi'a militias in the war against ISIS. Really. No one cares.
The hardcore Sunnis in Riyadh and so on will refuse to believe any stories of the Party of Ali not behaving with brutality.
Likewise, the mass of people in Iraq will refuse to believe any stories about their militias conducting atrocities.
Thus, it doesn't matter. No one can tell truth from propaganda.
Also, this is post-Speicher. Just saying. And if you dont know what happened at Camp Speicher, then you really shouldnt talk about ISIS.
Next, Assad. Similar to PKK, he has armed forces who will shoot at ISIS. Some of them better than others, to be fair, but the US will need to figure out if they are shooting at ISIS' forces, or if they are shooting at Assad's forces.