One concern with this line of argumentation: reasonable people shouldn't have to change their behavior, but rational people might want to.

That is, suppose you believe (as I do) that D.T. and his supporters are quite dangerous. If they are using my behavior to gain strength, it behooves me to change my behavior!

Sometimes, perhaps. But not if that change in behavior itself gives support and comfort to bigotry, deception, and authoritarianism, as it would here.