Or you could take the route which others have taken, and show them why their ideas are wrong through your actions. There are plenty of examples of extremists being converted through friendship.
They don't need to be rational for it to work. They can both either become more rational over time, or you can influence them in irrational ways. Both often go together hand-in-hand in good diplomacy (e.g. letting the other save face even if they don't "deserve it").
But equally there are plenty of examples of extremists killing people who are trying to show them why their ideas are wrong.