Why do people look down on others for having low paying jobs?

[MsMarvelDuckie]

Oh, GAWDS, yes! Been doing either retail or food service all my working life, and the view of the general public is to treat you like an idiot who can't understand simple orders or handle cash, or- anything, really. It's infuriating at times, and some days I just want to talk to them in the same condescending and insultingvtone they use. Like talking to a mentally challenged six year old. And there are people who are out in public driving and trying to order food whom I suspect really should be in some sort of institution or care facility. Yet we are the ones who are supposed to be stupid or incompetant....