Is it acceptable to ridicule people from "lower" socioeconomic or social classes?

While we’ve made considerable progress regarding certain groups (race, sexuality, ability, ethnicity, etc), it appears that many people are still ok with calling someone “trashy” or ridiculing people who come from a “lower” socioeconomic class. Do you feel that this is true, and if so – why?

I’m thinking about terms like: white trash, trailer trash, trash, trashy, low-class, etc used as prejorative. This can apply to taste in food, clothing, music, language, etc.

What are your thoughts?