I feel like I have to get on my soapbox again here: Tipping is a social convention, it's about noblesse oblige, and has nothing to do with reason. It is an art my grandfather taught me, and in learning to practice it, I find I have more reasons for appreciation than anger when I expect customer service. It keeps my life happy and low friction. I like that.

If you choose not to tip, that's fine, but trying to find reason in social conventions out of frustration of the practice won't make it disappear in a puff of logic.