I used to think the same thing but I've come full circle to believe that any behavior humans take place in, regardless of the consequences, should be legal and regulated opposed to banned/illegal. Money just ends up flowing to cartels and much more unsavory/unethical organizations.

Drugs, prostitution and even gambling fall into this category. It's certainly the lesser of two evils and not perfect. As others have pointed out I'd much rather live in a world that treats prostitution like Amsterdam or drugs like Portugal than the current war on drugs, police militarization, security theater surveillance state we are in right now.