"Deep dish pizza isn't real pizza!" 
Shut the fuck up. Pizza in the US is its own beast, its own culture. Real pizza was born and will die in Italy, every other pizza is a beautiful rendition that earns love and respect.
You know what deep dish pizza's aren't lacking? Sauce. Tons of pizza places, good and bad, skimp on sauce, leaving you with a dry experience. Sauce is used to bind shit together and nothing more in most cases. Deep Dish pizzas aren't lacking in the sauce department. Feels like you're eating tomatoes instead of tomato paste from a can.
Another thing that makes deep dish pizza unique, ingredients inside of a deep dish are easier to eat. It never feels like you have to give oral to deep dish pizzas, whereas some places stack and place ingredients in a haphazard way on "normal" pizza. Causing you to strategically eat so you don't get meat grease and veggies spilled down your shirt.
Pizza bigotry is special fellow behavior. Pizza is pizza.