This is the point where I could (in principle) accept the idea of "conditional collaboration" -- as in, "OK, I'll loan you, generally destructive and disreputable person that you are, the appearance of credibility, as long as you refrain from taking deeply harmful actions X, Y, and Z." That is, at least where there's some significant leverage exercised. And where "deeply harmful" means just that (e.g. backing out of the Paris climate deal, invading Iraq for no particular reason, etc -- something on that scale).

I'm still not sure I would have the stomach for it, myself, if I were in their shoes. But at least I could see how that could be drawn as an ethical position.