I sooooo hear you on this and relate. I waited tables all through college, and waitered and bartendered for years after college while my diploma was rotting away. I even worked as a room steward on a cruise line for six months, which took six years off my lifespan, at the least.
But anyway, when you are doing the waiting and the serving, you then understand the extreme difficulty of working in the service industry. It's basically a matter of empathy. And of showing your appreciation to a fellow human being.
If I was a betting man, I would wager that those who adanently refuse to tip have never spent a day of their lives in the service industry.