My experience is completely different(living in New Mexico). Sure some of the ghetto chicanos(born in America usually) can be slimey but the illegal people that I met in high-school and the older people I met working in the food service industry are often the nicest and most respectful people I have ever met, particularly the older women. They treated me like a grandson event though I barely knew them and we could barely communicate.

Edit: there's no way to tell which ones were and weren't legal but all of these people were straight from Mexico, obviously not all of them are legal.