I shouldn't be obligated to tip on food & drink. I know, I know -- you hate my guts. But I think my reasoning is pretty sound, so hear me out (or just head to the comments and start screaming):
The obligation contradicts the meaning
In theory, I “get” gratuity. The faster, smoother, and pleasant-er you bring me a meatloaf, the better chance I will gratefully reward you with money. It’s an incentive! That's capitalism, give or take a few multi-billion-dollar defense contracts.
But if my waiter knows I have to give a fiscal “thank you”, there’s no real incentive to do his job besides his normal wages (which he gets either way) and the look of pure joy on my face. Can I count on him to care about bringing me & this beef log together in a steamy, savory, gravy-laden union as much as I do? Maybe. Can he count on me to leave him 18% (or SOME additional amount) out of social obligation & good-heartedness? Yup.