I've been trying to upload a video about this for a while without avail, so let's try some text. I think movie theaters are so magical because they're one of the only public places in Western society where displaying emotion is okay. Movies are so emotionally evocative, and I just think it's so interesting that a group of strangers can go into see a movie and just kind of feel it together.
I saw Toy Story 3 last summer with a friend, and of course it made us weep like children. We're two people who absolutely hate crying in public, and yet here we were, faces wet, in a room full of strangers, and somehow okay with it. On the other end of the spectrum, laughing like hyenas is also completely accepted. I remember sitting next to one of my best friends during Bridesmaids and screaming with laughter during it, having to hold onto each other. But I knew everyone else looked just as crazy.
The range of emotions felt in movie theaters is something really special, which is why I so much prefer the older and smaller ones with character over the big megaplexes. They just have more respect for the emotional experience that is had when watching a movie within their walls.