I'm not sure I understand the scenario you have in mind, but I'll reply and you can elaborate if I seem to be missing your point.

I guess the scenario I'm concerned about is dishonest politeness. If I think someone is failing at politics, it is honest and polite to say "I would prefer not to discuss politics - let's talk about X instead." This case, and generalizations of it, are where I see the whole "let's not talk about politics" topic come up most often.

It would be rude to say "you've been mindkilled, stop talking about politics." It would be dishonestly polite to say "I'd love to discuss politics with you, but it's too hard for me, so let's talk about X instead."