When did it become a bad thing to think less well of people who are scum, criminals, moral lacking drain on society.
Is it really snobbery to look down on people because they are scum?
Personally I see snobbery as any people that simply regard themselves better for no reason. LIke a rich person who might look down on a doctor because he didn't go to Oxford and the like, or someone who instantly behaves rudly and instantly distrusts someone because they appear poorer, like someone who treats a waiter, shop assistant, plumber like scum because they aren't lawyers/doctors/bankers(lately, probably not the latter one

).
When you aren't a criminal, and treat people well, and think its wrong to knife people to get their wallets or for ****'s and giggles, are you a snob for thinking badly of those who do, and giving that group of people a name?
If you don't think yourself better than those people, if you don't look down on them and want to always be better than them, somethings wrong IMHO. If you think what they are doing is wrong, they you should naturally feel better than them, if you don't think you're superior to them, you probably don't think what they are doing is wrong in the first place, again, somethings wrong there.
It doesn't matter what started or what an original meaning of a word was, they change, people use words for different things and as slang. Chav is very obviously and widely used to describe, well, scum. Its not council house people, its council house people who act in a certain way, its not all criminals, its criminals who , I guess you'd say do a certain subset of crimes for a certain reason. Muggings for personal gain, or for no reason at all, murders, petty crimes, vandalism, etc, etc. I wouldn't really call a white collar crime person a chav, though I don't hold them in any higher esteem either.
The only people that seem to get upset by the term is those that say, maybe live in a council house, live around chavs but aren't one, but assume everyone thinks they are one too. Don't act like one, people won't treat you like one basically, its that simple.