Jeez louise, I said I agreed with you in principle and I explained why I don't do it in practice: perception is reality. I'm not sure how my difference in practice has devolved the discussion. Simply because it offends your sensibilities?
My point is simply something that I have learned over the years: It's okay to overpay sometimes, as long as you know why you are doing it.
Yes, the ostensible purpose of a good tip is to reward good service you have already received. Frequently, I am tipping in an establishment to which I intend to return, and in those instances I am also tipping well in hopes of receiving great service the next time I walk in the door. If I am known as "tipping calculator, no-tax guy" I don't expect that I will be greeted as cheerily next time as I am for spending a buck or two more. That, to me, is a situation when overpaying is worth it.
This reminds me of a similar dynamic: dining out with friends. One of my best friends since childhood is one of those who always either asks for separate checks, or he examines the group check to make sure he is only paying for what he had instead of dividing the bill equally among the diners. I get it: if I am ordering an expensive bottle of wine and you are not drinking, rest assured I will make sure that I contribute more, accordingly. But the "Um, I got the chicken sandwich and you guys got the salmon" business drives me insane. Another longtime friend is even worse: he will consciously avoid ordering wine in any restaurant because he insists it's more overpriced than any other alcoholic beverage, then he will enjoy a glass when the server pours it for him, only to later insist that he pay less than those who "ordered" the wine. We have come to avoid dining out with these people at all costs because it is so awkward and unpleasant.