I think you might find some solutions in a great negotiation book called "Never Split the Difference". Written by a former hostage negotiator. If you can negotiate with someone who thinks they are the Messiah and has a gun you might stand a chance online.

The problem is negotiation requires care and a lot of work. It's hard. And in public forums others will probably mess up your progress.

My best guess in a public forum would be to play the "good cop" and quote and defend the person I wanted to persuade. And while looking like I'm defending them, and being their friend, I would put forth an idea that is more moderate and thus move them towards being persuaded. This would be hard to do in the chaos of an online forum like HN or Reddit though.

Thanks I'll have to check out that book.

I agree, a public forum really complicates the issue.

I think one of the problems is that most people (who live in liberal-as-in-Locke societies) want the world to work on their terms, which includes rationality-as-they've-constructed-it. So most people want things to be "logical," or think people should respect "logic," while missing the points that logic must be grounded on premises that are taken to be true-in-themselves, that deduction can only be done after the fact to justify one's instincts, and that most statements can't really be posed formally anyway. It's better to think about rationality as a certain kind of intuition, where some things trip the bullshit alarm and prompt closer inspection.

I say this to answer the question, why don't philosophers and psychologists come up with good ways of convincing people of things? I think it's because they're blinded by their paradigms---as are we all.

As for how to change people's minds, I find that it only works if people are already unsettled about what they believe. How can you unsettle people? That's more of a skill that has to be discovered, and I'm not the best at it myself, but the answer probably revolves around really deeply exploring the other person's beleifs with them. Not trying to argue they're wrong, but just trying to figure out what their beliefs might look like if carried through. If you can manage to decohere their worldview, you'll probably get somewhere.