"Do you grant creationists good faith? How about anti-vaxers? Flat earthers?"

Yes. All of them.

I've never had to do so with a flat-earther simply because I've never met one.

But the others? Sure, I treat them like human beings.

Marginalizing people for their beliefs will not change their minds but it WILL fracture society. I think some people will side with the "opposing view" simply because they are indignant when they see how the sanctimonious mob treats them.