It really should be, if middle ages Europe, when the Catholic church ran everything, still tolerated prostitution as a necessary evil, then what's our excuse?
It's actually kind of barbaric that we don't tolerate prostitution in a safe and legal manner and instead leave it in the hands of criminals to exploit and abuse women.
Safe and legal prostitution is better than illegal and unsafe, it's going to happen anyway regardless of what anyone thinks about it, so why not go with the lesser of two evils?