Just to add to what Neil said....don't assume the rest of the world subscribes to your personal definition of oppression. Cruise ship jobs are considered lucrative in many countries, and nobody is being shanghaied to join the crew. They all sign contracts. I have lived in many poor countries, albeit for no more than 6 months in one place, but learned that what may seem bad to me is considered an opportunity to others.
So I don't dwell on it. I tip well when cruising, treat the crew with respect, befriend as many as I can, and have a good time. Leave the social baggage at home.