On your latter point, do you really mean that in the thought experiment of someone wanting to shoot your friend and coming to you to ask for directions, you hope you couldn't make yourself honestly belief falsehoods that you could then convey to the assassin thereby misdirecting him without seeming dishonest?

Indeed. As long as we're asking for superpowers, I'd prefer to have the ability to defeat the assassin, or to credibly lie to him without believing my lie.

Given that this situation is not going to happen to me, I'd rather keep the ability to distinguish truth from falsehood without epistemically poisoning myself.