I think the majority of men who use prostitutes would be embarassed to admit it - so just because a man denies that he does so does not make that a fact.
The reflex response - "I don't need to pay for it ..." is just that, an instinctive affirmation of a man's ptency and attraction - real or imagined.
For a lot of men, a simple financial and sexual transaction suits them very well, as the old adage says, "A man does not pay a prostitute for sex, he pays her to leave afterwards ..." and that is the essence of the relationship.
What is wrong about id depends entirely on the situation in which the woman finds herself.
If she is offering sex for money from her own home with free will, and is spending all the money she makes - no problem.
If she is an illegal imigrant being forced to pay back a massive loan and is effectively a sex slave being explouted and abused, then that is a massive problem.
Sex for money per se is not a problem - but how many enjoy the first scenario compated with those who ensure the second?