While some of the SO practices can feel dumb, I wonder what is the tradeoff we are making here? Could it be that for whatever reason (e.g. personality) we might benefit from accepting these "dumb" choices because it also brings with it unrelated benefits? For example, might it be that if they were forced to accept "frivolous" statements such as "thank you" (from the example you gave), might it cause moderators to not moderate, and thereby allow in spam & other nasty bits?

It is worth bearing in mind that if we, "good people", complain about moderation, we only see the parts of it that touch our "good posting". There might be plenty of good that moderators are also doing, which only the bad guys see.

"I was slighted once by a completely opt in community that helps millions of people every day so it deserves to die"

Why is this everyone's default response to this kind of stuff?

Between this and the reddit blackout, "volunteer" mods doing free work for a company are really overstating their importance. The cons don't outweigh the goods. It's why I like the Fediverse: I control what I can see on my own instance and don't have a rando telling me what I can and cannot do.