Without wishing to get into a debate about this (unsure why you quoted me when several people said the same thing..) I don't think people lack sense just because they don't choose to dress up for the theatre, there are no rules stating you have to. It's nice to make an effort I guess but if dressing casually will encourage more theatre goers I see this as a good thing personally. Whilst i've never worn a sweatshirt to the theatre I have worn jeans and even sneakers before, if people don't think i'm dressed up enough then that's their problem not mine. As long as people are respectful of where they are (don't talk during the performance etc) they can wear what they like as far as i'm concerned.