In every case it is a limited career that does not scale with age, while inculcating habits and attitudes that make traditional employment or switching industries difficult.
It's a popular opinion, but is it also true? For example sex professions aren't regarded specially in Germany or Sweden, do you think those people are damaging themselves more than any of the more "legitimate" professions?
Sex "work" is a "job" where the less experienced you are, the more "employers" will want you. What other job prefers inexperienced people? Only exploitative ones do.
Powerful, happy, balanced, rich people do not tend to work in the sex trade. Can you imagine Condolezza Rice or Hillary Clinton or Marissa Mayer deciding that porn or prostitution is what they really wanted to do all along but just could never find the time for?
You say this like these people are shining examples of people doing good for mankind. They're run-of-the-mill politicians. I couldn't care less about their porn or political careers. I'm sure the void would have been filled by someone.
Powerful people do not typically choose porn or prostitution.