I am against the concept of a customary 'mandatory' tip because it is false advertizing. The price of a meal or a drink should include the labour to bring it to the table. Restaurant/bar owners get a free ride from this practice. Yes, in a busy or successful establishment I'm sure it somehow balances out in the end. But in a less than successful establishment or a slow shift it is the employee who pays the price... not the owner.
It is also a wonderful way to fire someone without having to actually go through the hassle of justifying the cause. Just schedule them for the non-tipping shifts.
Tips should be an optional way to reward good service...not just competent service. I expect competent service... I want to be able to reward good service. A tip should mean that I had a really good time, thanks to their efforts. A tip shouldn't be just because the business is too cheap to pay a minimum wage.
/rant
Nevertheless, a tip is
expected in the US, so visitors
to the US should be sensitive of the common practices, just as you would expect visitors to be sensitive of the common practices of
your country.
The answer to the argument of "Why must one tip in the US?" is a simple one: one must tip, because it is expected.
The answer to the argument of "Why does the US continue on with this tipping expectation in the service industries?" is also a simple one: it is insanely stupid, but there is no way the large majority of service-oriented business will change their pay practices such that tipping is no longer expected. It's stupid, but we are stuck with it.
To take your customary tipping practice further, snberk... in Japan and other Asian countries, if you were to try to tip an employee for good service as you are wont to do... you would seriously offend that person, and their acceptance of a tip of that nature could affect their position in that establishment.
Would you disregard the common practices and expectations in a country like Japan and insist upon continuing your
personal customs and practices, even at the possible cost of a person's job?
Or, as I would expect someone who is sensitive of other peoples' culture and traditions, would you respect that culture's expectations and adjust your own accordingly?
That, is the point that leekohler was trying to make: you have to learn and act according to the common practices and expectations of the country that you are visiting. So, if you are a visitor to the US, you must adhere to the common practices and expectations of dining and imbibing in the US, just as you would expect a visitor to your country to do the same.
TL;DR:
Adjust your practices and beliefs to be sensitive to those of the country that you are visiting. If that means no tip is expected, then you don't tip (eg. Japan). If that means a tip is expected, then you must tip (eg. the US).
And yes, we know it's stupid. But there's nothing to be done about it.