Some people are forced into working in sweatshops to sew t-shirts. That does not make a good reason to criminalize t-shirts.
Forcing someone into doing something is already illegal. The forced person is a victim, most laws are clear about it. If the issue we are talking about is fighting against human-trafficking, the only question should be to know if legalizing prostitution would help the police find human traffickers.
And this should be the top question of the debate IMHO. I don't care much to live in a society that answers differently than me to the question "Should prostitution be legal?" but I would love to be in a society where human-trafficking does not exist.
I do have the feeling that pimps do enjoy the hypocrisy and moral ambiguity of the laws: it makes their services invaluable and their activities under the radar. But this opinion mostly comes from anecdotes and common sense. I am inclined to change opinions based on facts.
I disagree.
Few are forced to visit and hire a prostitute. But we know people are forced to be a prostitute (trafficking), some do it for drugs, and some feel they have no other way to survive. While society understands not every prostitute is in one of these categories, it seems a cruel punishment to charge them with a crime. MOstly because it would be charging a rape victim with the crime of being raped.