Whom shouldn't we talk to?
My tips for political debate were about how you should talk about politics, given that you're having a discussion. But some people said that, for certain political views, we should not have a reasoned dialogue at all; we should just condemn them. E.g., don't talk to Nazis; just condemn them, and maybe even physically attack them.
So whom should we not talk to? Here are some ideas:
"Don't have debates where the debate itself would spread information that shouldn't be spread." E.g., don't have a public debate about what would be the best way to execute a heinous terrorist attack. I think anyone would agree with this.
"Don't debate extremely harmful or extremely morally wrong proposals." E.g., don't debate Nazism. On this view, we also shouldn't debate Marxism, meat-eating, or drug prohibition. Granted, prohibition isn't nearly as bad as the holocaust; but if you're refusing to debate very harmful things, it's hard to say that the unjust imprisonment of millions of people is "not harmful enough" to qualify. On this proposal, it looks to me like a lot of political discussion would be replaced with trading bitter denunciations (I mean, even more so than in our current culture). Problem: No progress will be made! There will just be destructive conflict.
"Don't debate extremely epistemically unjustified ideas." On this view, we wouldn't debate with Creationists, Holocaust deniers, or meat-eaters.
"Don't debate ideas that are extremely harmful and extremely unjustified." Then we wouldn't debate, e.g., Nazism, Marxism, meat-eating, or drug prohibition.
"Don't debate bad ideas that lack social influence." This one differentiates between Nazism on the one hand, and Marxism, meat-eating, and drug prohibition on the other. The latter three all have clout in our society. This suggestion actually has some logic to it: if the idea lacks clout, then there is no need to debate it; in fact, debating it might have the effect of (slightly) increasing its clout.
"Don't debate people who are not open-minded." Objection: even when debating a closed-minded interlocutor, you can still convince people in the audience, readers/listeners who are not participating, of whom there will be many more.
"Don't have debates from whom no one is likely to learn." Sounds right. This could happen if there is no audience, or if the debate question is one on which people in general tend to be very dogmatic, or if the debate issue is one that all rational people already know the answer to (e.g., the flat earth theory).
Conclusion: Of course one should not have every debate that one can. But I think a very wide range of topics are debate-worthy, including many extremely bad and unjustified ideas. I mean debate-worthy in the sense that it might be good if someone debated them reasonably. I myself don't much like debating extremely unjustified ideas, and I especially tend to not want to discuss extremely unjustified ideas that lack clout.
To return to the example of white supremacists: I myself would not talk to them. But I found this podcast about a black man who decided to go talk to the Klan, and it proved to be very surprisingly productive: https://www.thefire.org/so-to-speak-podcast-how-daryl-davis-a-black-man-defeats-the-ku-klux-klan-with-open-dialogue/
So that's some evidence that dialogue (it wasn't really debate, but still dialogue) can be beneficial, even with people you would think there would be no point talking to.