As far as I'm concerned, no vice should be illegal. If the only victim of an activity is yourself, and you choose to involve yourself in it, and you're old enough to understand the consequences, what right does anyone have to stop you? Isn't individual freedom regarding one's body one of the basic principles of democracy, and the oppression of those freedoms one of the greatest grievances of american conservatives (the fight against Nanny Statism)? Prostitution, drugs, gambling, it's all in the same boat.
Where the problem comes, is when people start using the vice to exploit others - pimps, drug pushers, and loan sharks are the criminals whom vice laws should be meant to stop. The original intent of the Ontario laws mentioned by the OP, that were recently overturned, was to criminalize pimps by making it illegal to "live off the proceeds of prostitution", and to run a bawdy house. Unfortunately, that wording was vague enough that it could be used to prosecute the families of prostitutes, and also to people they hire, such as drivers and bodyguards, mentioned by the OP. So definitely the laws were in need of revision, though I'm not sure if there was anything put in to still make pimping illegal. I would prefer to see it simply covered under existing extortion laws. Though, in that case it would now require testimony from the victims in order to convict a pimp, I imagine. One big advantage of decriminalization is that now victims of exploitation can come forward to the police without fear of being charged with any crimes in the process.
It doesn't quite solve human trafficking, though, since victims of that crime still fear deportation if they come forward.
When considering the matter of vices, I usually look to the Netherlands as the example to follow. Nobody can claim that decriminalizing something will wreck society in their own countries, when other countries have successfully done it.
Someone mentioned the activity among animals as well, but I would be careful about making such arguments. What works for animals does not necessarily work for humans.
The reason we actually see a majority of women in this "business" is because we already have a disgraceful objectification of women in our society today.
Not so. The reason is the monetary value of sex to the average man is higher than it is to the average woman. Before condoms were invented, women had far more to lose from NSA sex than men did - 9 months under a severe physical handicap, and another mouth to feed when it's over. That's why they decided to attach the strings. The costs of casual sex may now be equalized with the invention of birth control, but the instincts are still embedded into everyone's brains that a man might compensate a woman for sex she wouldn't otherwise want. Objectification is tied to that, but not the cause of it. Objectification is more of the natural response of a man who aims to seduce his partners, when he sees that those partners can simply be bought by anyone with money or flashy status symbols. It's sort of a sour grapes mentality - why invest the emotion needed for a relationship with someone when at any moment she could go off with someone else who pays better?