In Europe, tips are not expected by the server. If you want, you can leave something extra if you want, but it isn’t by any means an expectation.
The US is system is the opposite. We have allowed a slave relationship to develop on the part of servers; they need to grovel and abase themselves to get the (maybe) 20% tip these days. I remember when it was a standard 15% not all that many years ago.
The problem is the system, and both restaurants and servers are responsible for it. If this were a sane system, restaurants would build service into the price of the food from the beginning, instead of playing the tipping game.
BUT THAT’s NOT THE POINT of this conversation.
It was originally “should servers be able to evade taxes on their tips”.
And the answer, again, is “they earned the money, they pay the taxes”. All the rest of it (low income, minority, less educated, blah blah) is just sophistry and rationalization.