His reasoning is that good guy’s AI will counteract bad guy’s ones or a an AI that has developed his own objective against humanity if that happens, which is I think a reasonable argument.
He effectively is arguing that the "good guys" will develop a superhero AI that will protect us simply because it feels that is the right thing to do. I'm not sure how any logical basis can be used to back that up, or where any meaningful example of similar behavior that didn't ultimately lose to the "bad guys" can be found in human history.
In the 20th century this same thinking lead to MADD and massive stocks of nuclear weapons that still present an existential threat to humanity. Depending on the scaling potential of intelligence this just adds further risks at this level, not less or balanced risks.