Why are sexual acts the 'buying of a woman's body' when paying for other services that involve the functions of the body (such as manual labour, assisting someone to wash themselves or excrete) or the spending of time (listening to a person, performing tasks to benefit or please the person) are not? Paying someone to engage in sexual activity doesn't mean that you own the person, or the person's body, any more than if you pay to watch the person dance, or have him/her paint your ceiling. The service is rendered, the bill is paid, and the person goes home.
Not everyone would be happy selling sexual services, sure. No one should do it against his/her will. However, some people would find it less morally distressing to sell sex than to work as a bailiff - or to scrub toilets.
There does seem to be an idea that preventing people from having sex is some sort of Good Thing, that it's bad for anyone to have as much sex as s/he would like.
Somehow I get the feeling that even if money didn't change hands and care home residents were joining hookup sites and having visitors pop round for NSA sex, some of you would want that put a stop to on the grounds that it's... Eeew! Icky! Old people/disabled people having sex! Make them stop it.