I agree.
However, as I've become more wealthy, I think of it as a (happily paid) extortion tax. _Fight Club_ taught me that the service class can anonymously hurt me. I strive to be overly polite and non-demanding, and tip 20%+ to be the good customer and avoid any vengeance.
I'm not cynical about much in life, but with tipping, I view it as cheap insurance.
Another commend focused on the difference between median wages and waitstaff wages - in my mind I tip more not because they make less, but because I have more discretionary income.