The objection that you don't tip your doctor or your lawyer doesn't really hold water.
Just as in a restaurant you pay for different aspects of your experience - food, clean table, refills of water, service of food, pouring of wine, explanation of menu items, etc - you pay separately in the US for your medical services. If you're having a baby you will get a separate bill from the OB/Gyn, the anesthesiologist, the hospital, the pharmacy, the pediatrician, the NICU and on and on and on. All of the medical specialists charge for professional services they render, and the hospital has a per diem charge which is itemised. Patients expect a heap of bills from everyone who was involved in their care. And there are plenty of lawyers, mainly PI, but also class action specialists, who work on the basis of taking a cut from a settlement or a judgement.
That kind of proves my point, really. You get separate BILLS from each provider; class-action lawyers work for an AGREED cut, negotiated and presumably signed for in advance.
You don't have an unwritten hope/expectation that the customer will give you somewhere within a range of a commonly-accepted additional amount - known as a tip, rather than contracted payment for goods or services - one that requires you to argue/get angry/challenge/humiliate yourself if it isn't paid (or not as much as you were reckoning on), rather than simply threatening/beginning legal action for provable breach of contract.
I don't object in any way to paying a fair amount, and I do not condone people who refuse to take part in the way things are and refuse to tip, when that is the accepted way. I agree that the whole tipping culture IS subsidising employers, but the answer to that is not to take the service anyway and then punish the server for the system. My beef is purely with the method of charging, whereby prices are not clearly agreed and assured as part of a normal transaction.
I'm fine with charity/community projects that, instead of having prices, just invite people to pay what they want or can afford; but then, you can't get angry with people who do just that, when what you said isn't really what you meant.
This thread is going around in circles - some people are claiming that serving staff can only just survive with the tips and others are saying that they wouldn't want a more straightforward agreed-price system, because they can make lots more from tips. It just adds even more confusion than already exists.