You're presenting a logical contradiction : strawman.
If one is to believe man is good, man will act in good ways no matter the incentives.
If one is to believe that man is neither good nor bad but behaves according to incentives then one would try to fix incentives.
You're saying that people who try to fix incentives believe man is good. That can't be true.
Prime example : Bitcoiners believe people are greedy, which is the basis for a good portion of the security model.