Laughing during a movie is impolite? That's insane. So if somebody makes a joke you just sit there stonefaced like a psychopath?

The ones near me have been pretty well-kept, but I imagine it varies by site. Either way, I fail to see how laughing at jokes means we don't care about each other? I usually feel a sense of ease and connection when a theater collectively laughs quietly at a funny moment. A messy theater existing somewhere doesn't change that moment into a bad one.