Expectations of politeness generally involve letting people have their happy delusions if they aren't harming anyone. For instance for someone whose son went MIA in Vietnam and holds hopes that he will return one day telling them "He probably either died and his corpse was forgotten or in the off chance he is alive went AWOL with some peasant girl after getting fed up with the war and lives in fear that he will be found out.". Even if statistically it is 100% true that would be staggeringly rude to say to them.

So what? What I am saying is that there must be other possibilities. Even 1 person who is kind and honest would be enough to render what I said correct.

I was reacting to @stemc43 who said "I'd rather work with...". Why wouldn't you rather work with kind and honest people? If you are picking your ideal scenario already anyway why not pick the positive version instead of the negative one?

So what? There are also non benevolent lies and polite truth.

We just call those "lies" and "truth", and that shows us nothing because it was never in doubt that truth and politeness are often not in conflict.

On the other hand the idioms identified point to a long-standing understanding that sometimes, they are in conflict; a corollary of which is that one who always chooses complete honesty has likely failed to be polite from time to time, and one who is unfailingly polite has, like the curate describing his egg, likely given less than the total truth.

Most of us tend towards the politeness side of the tradeoff - we might, for example, describe a potential process failure when a more honest appraisal is that carelessness was the root cause.