Yes, I think there is a lot more potential for exploitation on many levels. And that can be a good reason to ban or regulate an industry. And for that matter so can the direct danger, if the work itself isn't important. So in that view the work might be legitimate but isn't worth the risks involved or the cost to manage them on a societal level. Enough so that it is ok to restrict people's freedom to do the legitimate work.
For me, the most important idea is totally diferent, I think it isn't legitimate work, that it comes down to selling, or gifting, children, as if they were possessions. Which more and more seems to be how our society thinks of children, but fundamentally it's wrong.
If you can't sell or give away a person the whole basis of surrogacy comes apart. In a way it doesn't with adoption which is about duty of care and how that is managed when the parent is unable or unwilling to take that on. It's really society and the state making accommodation to fulfil the needs of the child and his or her rights as a vulnerable citizen. It's not about the parents really, either the biological or adopted ones, its not done for their good, though that may be the accidental effect.
In surrogacy it's a transaction of a person created for that purpose, and separated from elements of their most intimate human relationships. All for the good of the adults making the transaction.