Brilliant!
You and dreamingjewel between you have articulated what so bothers me about the so called "anti-racism message" in these books. I don't think there is any doubt at all that James Potter was, in fact, racist and never examined his own assumptions. At the very least, he was deeply prejudiced against Slytherins. And, as I said in the other thread, in the Potterverse, you are born Slytherin and have no real choice in the matter. It's as if Aunt Marge was preaching the mantra of the entire Wizarding World - blood will tell.