Why is prostitution illegal?

The moral attitude toward sex or sex for sale is still flying high or is it. Gay marriage is legal in most states. They are legalizing pot smoking slowly across the country. A man and a women can meet in a bar have a few drinks and go home and have sex. This is all legal, but to pay someone to have sex with you is illegal. Why is that? You can hire a woman to go on a date with you, but if you have sex that is illegal. Men pay women for sex and so do women pay men for sex.

Follow my thought on this, A man asks a woman out to dinner he pays for it all. When he arrives he may bring her flowers. He has spent money to take her out to dinner and if they both agree they will have sex. Why this type of prepayment is legal but cash changing hands is not.

My thoughts on the subject the hold up on legalizing is that the government cannot figure out how to put a tax on paying for sex. If the government: either federal or local can find a way to put a tax on the selling of sex. Then they would vote to make it legal.