I tend to agree with this. The previews are one big commercial. They're not setting the scene, they aren't part of the story line and most theaters don't even have the lighting all the way dimmed during them. Once they're over? Then it's rude as hell and scream worthy. But during the previews? CHILL OUT.
On a side note, I never go to the movies because people always manage to be annoying one way or another regardless. And it's expensive as hell. I like drive ins though. Those I can do.