Is politeness about pretending to be weak and having the other person pretend to be weak too?
Zeroth problem: pretending.
First problem: how about pretending to have some self-respect instead of pretending to be a cringing weakling. Let's all pretend to be as unhealthy as possible. Fake it till you make it, right guys?
Pretending to be weak is a weakness. Like all forms of pretense, it's exploitable. If I decide to prey on them, they either have to drop the pretense, admitting they're a liar, or let me gnaw on them. Any form of defence other than admitting to liarhood is itself exploitable. "What are you so mad about? I'm not doing anything."
On the other hand gnawing on such stringy prey isn't worthwhile. Block polite posters. Sage polite posts. Report polite threads.