And if I'm "best at" creating dissonance, hindering scientific research, or some other negatively-valued thing? If I should do the thing at which I'm most effective, regardless of how it fits my utility function...

I don't know where that's going. I don't feel that's a positive thing, but that's inherent in the proposition that it doesn't fit my utility function.

I guess I'm trying to say that "wasting my life" has a negative value with a lower absolute value than "persuading humanity to destroy itself" - though oratory is definitely not my best skill, so it's not a perfect example.