I always tip because it's the convention and I'm afraid of being confronted about not doing it. If I didn't have that fear I most certainly would tip far less.
You should drop the stuff about selfishness. It's self-interest. Everyone agrees if you define "selfish" as not doing anything that could possibly aid anyone else then human society wouldn't work. Clearly you'd live in a cave and have a subsistence existence until you're dead at 15. I don't know anyone who actually advocates that. So the definitions must be off.