Why are people mean to autistic kids?

I was going to Burger King in Garner, NC and the cashier/manager was laughing at my brother. He is autistic and has a learning disability. I told my brother that we will not eat there again because the cashier/manager were mean to him. I think it is rude and inconsiderate to be mean to kids and from now on i'm cooking meals for him. In this day in time, restaurants should treat every customer with courtesy instead of disgust.