If someone shouts, "2+2 is not four! It's something else!" Is it polite to stay silent?

Calling it polite is specious, isn't it? Is it considerate to withhold criticism in the face of lies and untrustworthiness?

I think this conflation of non-confrontation with polite is really something quite obscene. Doesn't this equate self-censorship with consideration? What's being considered when you think "well this is stupid, it's obviously 4 and I have no idea why someone would yell something that silly - I suppose no one should take the carnival barker seriously enough to even acknowledge this".

That is not politeness. That is providing permission to spread ignorance.