Note that Tipping norms vary a lot from one culture to another:

• In the US, if you don't tip at restaurants, you're being a major selfish dick

• In France (and China, and as far as I know most of Europe), tipping in restaurants is optional, for good service

As a result, American servers don't like having European clients, because these often don't know they're expected to tip.

So different people may be approaching the subject with different preconceptions about what tipping implies about morality (I'm thinking of lucidfox's "Tipping is voluntary. If you want to do it, do it. If you don't, don't. There isn't anything inherently altruistic or jerkish about either scenario", which would probably sound wrong to an American). I assume the OP was talking of tipping in an American context.