At some point you need to act based on what is right, not based on geopolitical calculations and game playing.  The right thing to do is to recognize that Erdogan is a megalomaniac, an extremist, a man with no respect for democracy, the rule of law, or human rights.  So cut him off. Kick him out of NATO.  No access to the EU without visas.  Duties on all Turkish imports.  Let Putin be his buddy.  They deserve each other.

What goes around comes around.  Guys like Erdogan eventually get so caught up in themselves that they don't see their downfall coming.  When it does, Turkey will come back into the western fold.