I look down on them because of their widespread bad business practices: the majority of the time you can expect price gouging and poor workmanship. They'd be better off working for Microsoft with that attitude.
I'm sorry that you have experienced the worst side of the human experience. It has certainly not been mine. Yes, I have encountered the occasional scammer, but by and large the tradesmen I have had direct contact with have been honest. I have heard people complain about the $50/hr plumber or mechanic, so they hire the $20/hr guy who comes in and does a crappy job, then they end up paying a competent worker the 50 bucks an hour anyways to make it right.
If you hire someone who takes you to the cleaners, you have a right to be upset, but if you failed to get references, and do your research, you have to accept some of the blame as well