Rationality is a win for the rational agent. But in many prisoners-dilemma and tragedy-of-the-commons scenarios, having rational agents is not a win for society.

It's not just social dilemmas that can favor "irrational" morality; an imperfect consequentialist agent may do better according to its own values by adopting non-consequentialist ethics. I question that this is actually "irrational", per my interpretation of "rational agents win".

If you decide to be a fanatic, you should tell other people to do so, too.

What if I believe that an individual's utility-maximizing level of fanaticism is proportional to their reasoning ability (or something similar), and that my reasoning ability is much higher than average?