Economics should be subsumed under the general study of human behavior, not the other way around.
...The conceptual differences between leaving a tip and paying income taxes are not as large as they might first appear. If tipping were under the aegis of complex bureaucratic regulations and income taxes were based on citizens following the custom as they best see fit, we might resent the former more than the latter. As it stands today, tipping is much less unpleasant, because you do not have to fill out complicated forms. But if we were to become convinced by a Stiglitzian demonstration that tipping requires regulation, then you can be certain that in order to calculate our obligatory tip, government would force us to fill out forms detailing how well the waiter explained the menu, whether the food was served sufficiently hot, and so on.
Although a libertarian would argue that the government obtains tax revenues at gunpoint, the fact is that most people pay their taxes willingly. In fact, I can imagine a government being entirely supported by voluntary contributions, in which citizens make their payments on the basis of habits, beliefs, and values.
You may need to read the entire essay to get the context.