For GiveWell in particular, if you do not believe they can do this, why do you think they can evaluate other charities' effectiveness?

Yeah, I think that's right. I'm the same as people who don't want to give to charities who have too much "overhead," leading to perverse incentives, as you say. GiveWell itself can be looked at as overhead for the charities it recommends, even though technically it's a different organization. As such they deserve to be supported too.

Will click "Unrestricted" in the future.