How many prostitutes have you known, Luissa? Most of them started out by being forced. They almost always have sexual abuse committed against them when they were very young, which warps their judgment and their egos. Only a tiny percentage willingly and happily stepped into that condition.
Besides which, in purchasing the services of a prostitute, you are renting a human body, to do whatever you want to it. And that is slavery. Prostitutes (in the US) are generally drug addicts for one of two reasons...they became addicted and then fell into prostitution as a way to pay for their habit...or they started using drugs to make prostitution more palatable.
In addition, prostitution lends itself to slavery in the most traditional way....men and woman control groups of women, rent or sell them, and make money of the proceeds. I have worked with a woman whose earliest memories are of her mother holding her down when she was about 3 years old while a man had sex with her. In return, her mother received money and drugs. At the age of 9 she was sold by her mother to an old man, and lived with him, completely hid from the world, for the next 7 years, until the man ended up in the hospital, and the hospital staff upon his death asked her who she was.
She had no identity, had never been to school, had no social security card. She had never been to a doctor, and at 16 all her teeth were gone. They had to conduct a long drawn out investigation to even figure out what her name was.
This was in the US, and it's not uncommon. We have slaves smuggled across our borders all the time, and forced into prostitution in this country. They're throw away people. They use them to smuggle drugs in (children who are smuggled across with bags of dope in their guts. YOUNG children.) then sell them into prostitution until they die or are killed.
We should never, ever support trafficking in human misery and death, and that's what prostitution is. Whether it's legal or illegal.