@Edgar makes an interesting point about global economies. In my service experiences, I've met folks from all over. Part of my job required I "train/experience" all positions. So at different times in my career, I worked as a server, a hotel room cleaner, a cook, etc. I have a lot of respect for folks in those jobs because I was not good at any of them. My "best" position was probably washing dishes.
During one of my "dishwashing experiences," 20+ years ago, I met Ahmed. He was from Pakistan, in his mid-40's, and although he was my trainer, his English was a challenge for me. He was smart, organized, and a hard worker. This store did $85000+ a week in sales so there were 10-12 dish personnel on the busiest shifts. At times, the dish room was staffed with citizens of Pakistan, India, Iran, Iraq, Mexico, etc. Ahmed was a leader in the group and sometimes had to "keep the peace." I quickly grew to admire his handling of the many diverse cultures.
On a break, he asked me if I was "the boss." I said, "I'm A boss" but deferred to the in-store mgt staff. He got quiet and I knew something was bothering him, so I asked him about it. In broken English, he explained to me that he needed time off next week. Even though he'd asked weeks ago... he was on the schedule. He did not want to lose his job, but he really needed the time off. He was able to get time off from his night job (Thus, I discovered he was working 80+ hours a week). Trying not to step on my manager's toes, I simply asked him, "Why do you need the time off?" His answer floored me... He said:
Mr. Ron, I need to go to New York, to Cornell University, as they have asked me to do a presentation.
Turns out in Pakistan, he had a doctorate degree and was published and well-regarded in his field. Yet, there was no job available to him in Pakistan (never found out why), so he came to America. Unable to get a job in his field due to his English, he told me he made more money washing dishes than he made in Pakistan. He was sending money home to his wife and children and hoped to bring them to America one day. Needless to say, we got him the time off. Weeks later, I received a thank-you note that I am sure was painstakingly written with an English dictionary close by (This was long before Google translator).
Ahmed left his country and his family to try and build a better life. From his perspective, it was better for him and his family to wash dishes in the USA than work in Pakistan (His issues were deeper than just money, but I never found them out - he was a proud and private man). His story made an impression on me and the now, "in the know," mgt team. They helped get Ahmed into an English training course and eventually - and good for him - he left our company. Unfortunately, we lost track of him but I know he became successful, on his own terms.
There's no doubt that that are many inequities in the world. And yes, tipping is one of them. As noted in this thread, there are many opinions. When to tip IS confusing and driven by many personal factors. I understand those who say. "The concept of tipping is not consistent with my values." Yet, my response would be to think in terms of the person receiving the tip and educate yourself on the local customs and tipping rules before you travel.
For example, if you are not from the USA - and you don't tip in your country - when you travel to a USA region where a server makes $2.25 an hour, what statement are you making by not tipping? It's not the server's fault. She's got kids at home, bills to pay, a car that needs parts so she does not have to walk to work, etc.
If you disagree, work to change the system. If you cannot or will not, then you should probably tip according to the local custom - whatever the service position. Certainly, the function of a forum like this is to exchange ideas and I think we all learn - respectfully - from everyone's experiences and perspectives.