Obviously, Primetime...we do not tip receptionists, gas station attendants and the store clerks. Nor do we tip the mail carriers or the guy who checks our meters.
We all work hard for our money. I doubt anyone here would say they didn't. So I will not mention the "hard work" cruise ship staff do.
However, if in good conscience you can accept gracious service from a person making a dollar a day, and fail to recognize these people beyond a simple "thank you" and I hope you are not stingy with those, that is your business.
No one will jail you for bad taste if you refuse to tip. That is your choice. Just know that you are not "getting away" with anything by not tipping. Nor are you really "saving".