This is actually kind of hard for me, I'm not normally used to being conservative on social issues, but I don't think we properly know what the long term or far reaching effects of something like this would be. I think China's one child policy is the best example of this. Who would have thought a one child policy would lead to sex descrimination in abortions leading to a glut of men without wives which could potentially result in population collapse?
I don't think most people think of these things when it comes to sudden social changes in legislation.
Probably not much. A very small percentage of women are willing to work as prostitutes and a small percentage of men are willing to rent them. It's a niche industry. Having the government not care what reasons adults have for agreeing to consensual sex with each other isn't much of a social change.
Here in Canada, a bunch of prostitutes complained to the courts that the current laws were making them more dead than they'd prefer to be, so all the prostitution laws got thrown out ... or put in some kind of state of nebulous uncertainty where just nobody got arrested or something. The net societal impact was that nobody noticed anything except for the prostitutes who ended up alive a bit more often than before. Amsterdam is a fairly regular city outside of a few blocks and hasn't experienced any kind of population crash. Las Vegas goes on being a normal place once you get away from the Strip.
There doesn't seem to be much in the way of justification for this sort of concern.