Why do northern people think southern folks are stupid?

I'm from Alabama, and we have a lot of northern visitors come down here and their very disrespectful to us! I work at the local diner to earn extra money. They can tell I have an accent and they start talking to me like I'm stupid and can't understand them. It really pisses me off! I go to school, I get a education. But why is it that just because I talk a little differently I'm considered stupid?