I'm American and a former waitress. Let me explain some of the math and why servers do get upset when people don't tip.
I used to make $2.60/hour, that was less than half minimum wage (and in one of the country's most expensive cities to live in).
I didn't even see that paltry $2.60 though, it went straight to paying the equivalent of my PAYE/National Insurance contributions. Every paycheck I got was for $0.00.
So really, my only income was tips. Of the tips I received, I had to pay out 20% to other staff (like the bartenders).
The government taxed me on the assumption that every night I received tips equivalent to 12.5% of my total sales. It didn't matter whether I actually received that amount or not.
I do understand why people resent having to help pay our wages. I think it's probably less annoying than having to pay $20 for a burger though, which is what would happen if servers were all paid living wages instead. Restaurants/bars almost always operate on very thin profit margins. If you think about having to pay, say, ten staff a night (for a smallish place) double their usual wages, of course prices would go up a lot.
Oh and please remember that unlike in the UK, most US servers will not have access to cheap healthcare, sick days, or any other benefits.