If this was true, why are the history books littered with so many evil people who gained power?
This isn't a rhetorical question, by the way: If you can prove that being smart actually does necessarily come with ethics despite that observation, that solves a whole category of doom scenarios.
(Not all doom scenarios, because we still have the "what if AI is only a smart as those specific evil people" or heck, "what if AI is only as smart as cancer, killing its host" scenarios; but it helps a lot for the foom-then-doom cases).