alright, so from my personal experience, most of the private school kids I have interacted with that were not close friends beforehand, have been total dueshbags towards me. They love to 'look down' on me for going to public school and shit like that.
so, that is why i judge people on it... because from my experiences (not just a couple, a lot in fact), lots of them are asshats.
BUt I can understand how it could be different for others.