I think the servers make a pretty decent living on the ships given the fact they don't have the normal expenses we, as home owners, have. No lawn fertilizers, garage door opener repairs, mortgages, taxes, washing machine repair, plumblers, trash pickup, etc. It clearly states on their web sites waiters earn between $2300 - $2700 per month.
But that's with tips of course. If we stop tipping they stop serving. If they stop serving the ships stop sailing. They stop sailing we stop cruising.
One way or another, we will be paying for their service. I'd rather have the choice of how much to tip rather than it be added to the price of the ticket.