Hello DrydockOkie,
Well that argument is so old around here, it has dust on it. The standard answer to that, is to remind you that the tips the shipboard workers receive are not "over and above" their pay. The tips essentially ARE their pay. They only receive a very, very tiny token salary, and the rest comes from tips. You receive the benefit of their labors, thus you "tip" them (essentially you pay them.)
It's just like in a restaurant, you know that the waitresses only earn a small wage from the management. Their real pay is the "tip". It's not really extra. It is an understood agreement between the customer and the server.
The proof of that is the fact that waitresses have to pay income taxes totally an amount equivalent to 8% of the restaurants sales, whether they receive that income or not. So you know that anyone who does NOT tip a waitress is in actually fact, not only taking the waitress's labor without paying for it, they are additionaly, taking money directly out of her pocket.
It's an antiquated way of doing business. But that's the way it is.
And so it is on the ships. You can increase or decrease a bit to match the service level. But remember that when you go to work, you don't expect your boss to say, "Gee, you didn't do anything extra special at work, so I'm not going to pay you this week." If you did what was expected of you, you expect to be paid. Why should the expectations of shipboard employees, be any different than yours?