The problem is that it's the norm in the US. If you have a service job (waiting tables, delivering pizza, etc) that's just how it works. You'd have to change the type of work you do because it doesn't differ much between employers.

Aren't there any unions for the these kind of jobs?

It's very hard to unionize. I ran a pizzaria for about 10 years and was the owner operator it for another 5. The employment length of tipped employees typically is around 6 months. With people coming and going so quickly, it's hard to develop the bonds that allow such organizing.

For positions filled people that are completely replaceable in hours, including finding and training them?

The answer might be obvious to you, but it is not to me. That's why I asked..

It is terrible, but it's the system we have here in the US. I'd like to see it changed, but in practice, if I'm at a restaurant that expects a tip, I am nearly always going to give a 20% tip unless the service is really subpar. Some people would argue that's too high, but I've been out with one too many people here who have a "well, the waitress took too long to get my check to me or misread a menu special item, so cut her tip in half" attitude.

And why is it your responsibility to compensate for bad customers, instead of their employer?