The immediate benefit of decriminalization is sex workers being able to go to the authorities without fear of reprisal when crimes are committed against them. After that, the greater the level of organization the greater the cost. While a freelancer's tax burden is what she declares, a licensed business can't dodge that easily. And if you have to provide healthcare to your workers, the cost is going to be higher given their work and because we have the highest healthcare cost in the world.
And after it all, you still don't have any barriers to human trafficking despite being "legal", so it doesn't solve that problem.
So it's either all illegal or it's legal and government is just as involved as in any other business.