When you go out and eat, are you obligated to tip your server?
I feel very strongly against the way the concept of tipping has been corrupted that leads to the question in the first place.
If it is any kind of obligation, it isn't a "tip" by it's proper definition. A tip is meant to be a
bonus payment for
exceptional service. That should be an entirely free choice by the customer, not a socially (and sometimes formally) expected or even required payment and amount.
It has long being used by employers as an excuse to maintain poor levels of pay in many areas of work, relying on tipping to make up the difference. I gather in America, this can go as far as having a lower minimum wage for employment groups like servers, on the assumption that they'll receive a certain level of tips. Sometimes this extends to back of house employees too though, who wouldn't naturally be expected to be tipped (though they may well be the ones putting in the effort that earns it).
There are a whole load of problems with this process, including inconsistent ways in which tips are actually received by staff (if they are at all), tips not being declared for taxes and the expectation of an automatic level of tip leading to conflict and resentment (as you described). There can also be ridiculous contradictions due to "tips" being a defined percentage of the price of the meal. Carrying a lobster and a bottle of champagne is not more effort that carrying a salad and a bottle of water but the first would likely involve a much larger tip.
Restaurant owners like it of course because it allows they to list the prices of their food lower than it actually is, with an expected gratuity percentage in the small print. I've always seen that as on the borderline of fraud, something that would be unacceptable in most other areas (and probably illegal, certainly here in the UK).
I could go on but I think there is a word-count limit here
. I generally tip the "expected" amount when I do eat out (which isn't often) because I don't like conflict and I don't think that helps anyway. To improve the situation would require some form of systematic change, either by the industry as a whole or driven by government. Unfortunately, neither are going to happen.