Devil's advocate: why should they be selective about who they receive donations from?

Obviously they shouldn't name a building or something after the guy, but, to give an extreme example, would it be a problem to take money with no strings attached from a serial killer or war criminal?

Edit: Okay, this is a pretty good answer: https://news.ycombinator.com/item?id=20963945. I mean maybe it could be an acceptable solution for them to make a public statement like "we hate this guy but we're taking his money anyway", but having no association whatsoever is probably safer.