I call them "men".
Women have strong biological reasons for being very choosy about their sex partners, while men have strong biological reasons for being indiscriminate. Humans grew so accustomed to seeing that as "the way it ought to be" that they built social mores around it.
Is it fair? No. Is it right? No. Is it natural? Perfectly.
I have strong personal reasons for not lying with prostitutes--Mrs. P. would frown upon it--but I don't see prostitution as morally wrong, nor prostitutes as wicked, and I would not shun them in non-sexual contexts.
(Questions regarding how-would-I-feel-if-my-daughter-etc. cheerfully ignored.)
Well, most morality comes from a belief in God.