I believe in both.. a fair wage and tipping for service..
I think that the situations you are describing are horrible and should not be condoned.. the tip should not be part of the baseline of a living wage or something someone should have to bank and calculate their life based on. it should be cash in hand above and beyond that as an individual gesture of appreciation of the service received.. I don't know I guess the whole obligation factor throws that out the window though..
I don't know for me it's what I do because I appreciated it when I was on the other end... not something I do to try and enable the bastards to keep folks down but I see how it's not cut n dry.