Everything is what it is. Sex work is different from carpentry and it is different from surgery. It is like carpentry and surgery in that it is a way of renting one's body. It is like surgery in requiring some hardening and compartmentalization. It is not like surgery in that it involves a different set of skills and different emotional preparation. A distinctive thing about sex is that it involves taking pleasure in ourselves and others as physical things, as objects. Very often we enjoy being objectified. We like to feel sexy, to arouse others, to be wanted qua object. But the danger of objectification is de-subjectification: losing track of the fact that the other person is not only an object, to be used as a means to one's sexual ends, but is a person — an end in themselves. Sex workers, like models, are paid to be de-subjectified to some degree, to be used as means, and this can come as a blow to dignity unless one has braced oneself against it.
I find it a bit insulting to feel pushed to have to say that children are not prepared to brace themselves in this way. Or to feel pushed to say that parents have deep, special obligations to attend to and protect their childrens' subjectivity, to cultivate and protect their personhood as it develops, to cultivate and protect their burgeoning sense of dignity. For a parent, of all people, to de-subjectify a child, and to use him or her as an object — as a means for sexual gratification — is a special kind of betrayal and violence. I'm sure we can all agree to that. And from here on out, I'm sure we can all agree that we are not talking about children, but the activities of consenting adults. We are talking about whether paternalistic prohibition of these activities may be justified.
A large part of my point is that adults are not children. Laws that insist on treating women (in particular) as children do not benefit them. Again, it is important to point out the circularity in this perennial form of conservative reasoning. We cannot infantilize a class of people by denying them their full autonomy and then turn around and appeal to the fact that we have done so as justification for paternalism. (Read mid-19th century debates against the abolition of slavery to see the most egregious examples of this form.) We've come a long way (baby!) from when women were treated by the law like large children for almost all purposes, but we still have some way to go.
There is nothing unique about work that requires those who do it to cultivate distinctive emotional strategies that make it possible to do things that might otherwise be off-putting while leading a completely healthy, normal, happy life. Some people find cultivating certain attitudes easy, and others don't, which is why not everybody is cut out for every kind of work. Personally, I think I would probably find it easier psychologically to sell sexual services (in a world in which this was legal and not despised) than to sell cars, since I find the kind of subtle manipulation one must practice in order to be a successful salesman completely intolerable, but I don't particularly mind being treated as a piece of meat. I'm sure there are a lot of sex workers who aren't particularly well cut out for it, and who find it really taxing, but who do it anyway because they don't have better options. I feel terrible for those people, but I certainly don't think we would be hurting them by making their profession legal and less despised.