You might be surprised at how many servers there are who have the same attitude as I do towards tipping/not tipping. The servers I worked with felt the same. And I belong to a couple of serving message boards and most of them feel the same. Thankfully, I no longer work in the restaurant business but when DH and I go out to eat, we always leave a tip unless the service was really terrible. But as a server myself it has to be really, really, really terrible for us to not leave anything. We know that tipping is how the server makes her money. If we couldn't afford to leave a tip, we just wouldn't go out to a sit-down restaurant. It wouldn't be fair to the server.
Thats why I said "if they demonstrated that attitude". Tipping is not about what the customer can afford, its what they are willing to give for the service they recieve. If I recieve terrible service, I don't have a problem not leaving a tip. I don't feel bad because thats how the server makes their money, if they need that tip then they better give service deserving of a tip. If they have the attitude that they are getting a tip anyway so who cares what kind of service I give, then I have no problem letting them know it doesn't always work that way. Now I have never not left a tip, however I have left as little as 10% because of horrible service. If you aren't willing to work fo rthose tips that you need, then you need to find another line of work. Nobody owes you a tip because you are wearing a uniform and have a name-tag.

and several cities nearby. Nothing like where I live now though. (Northern VA)