I would find it moderately annoying but so long as they're quiet and just commenting on the various previews and not actually carrying on a conversation I wouldn't tell them to STFU.
Based on your subject line, I expected to come in and say, "Uh, there isn't any movie theater etiquette anymore!". But previews are often my favorite part, so I hate when people talk through/over them.
I'm curious about this. A man and his son talked through the movie, even though two people asked them to be quiet. I feel like it's just a thing now that people do what they want, totally disregarding the other people around them.
I think you're going a little far on the extrapolation. There have always been assholes who talked at the movies. It's not a symptom of some new epidemic.
Don't get me wrong, there are ways that society has gotten more self-centered and less considerate. But I also think people (myself included) tend to take a legit complaint (asshole talkers) and turn it into a Sign of the Times.