The moral and ethical side needs to be considered separately from the practical side. There are two questions.
Should the sex act be sold for money?
If sex is performed for money, then how should that sale be conducted?
I don't even know an answer to the first. In an ideal world, every man and woman sould have a loving partner, with whom they have a joyful physical relationship which fulfils all their needs, and no-one is driven by frustration to buy it, take it by force, or sublimate the need for it into twisted violence. Yeah, right.
A brothel is not something that can be easily managed by your average business man or woman. It takes someone who knows the practical side of the business from the bottom up, so to speak, but has intelligence and management ability, skills with money to keep it maintained and the bills paid, a formidable enough presence to deal with any client who oversteps the house rules, the diplomacy to talk to people in authority, humanity toward the girls who work there.
These are not qualities that are associated with many brothel-keepers.
In Edinburgh there used to be a brothel run by Dora Noyce in a house at 17 Danube Street. Its presence was common knowledge. Take a look on Google Earth for the kind of Georgian town house, and in the property pages for the current prices of such houses.
It thrived for 30 years and catered for all classes. Apparently it did a lot of business during the Festival and when the Assembly of the Church Of Scotland ministers were taking place, and the busiest time ever was in 1970 when the aircraft carrier USS John F Kennedy was docked at Leith. The queue of sailors went right round the corner into Ann Street.
The girls were well looked after and any trouble was quelled at once. Any neighbour whose property was damaged by an impatient drunken would-be client was compensated at once. Mrs Noyce was arrested from time to time and charged 47 times for living on immoral earnings. She paid up her fine, went home and got on with running the business - a prim-looking little Edinburgh Tory lady in twinset and pearls and fur coat.
When she died, the girls continued to work in the house, independently and without the administration that she had organised. There was more noise, more violence, more trouble with the police. The house came to be viewed as a public nuisance, and finally closed down in 1977.
The ORDER that had been kept had gone.
Then there are those who don't wish to sell within that order, or to buy within that order, and those who want a perverted service which only those most in need of a few pounds will submit to.
Regulating ALL of this traffic would be a gargantuan task. How do you regulate someone who puts out on a casual basis when she doesn't have the rent? How do you regulate a punter who knows that his request will not be on the price list of a respectable registered establishment which looks after its staff and is aware that regular inspection will reveal the scars and bruises?