I could just as easily propose contracts for sales of kidneys from living donors. You have 2 of them, after-all, and if you happen to be mentally incompetent enough to sell one of them for a few bucks, who the heck does the guvment think they are interfering, eh?
EDIT: See http://slatestarcodex.com/2013/08/25/fake-consensualism/ for some more background.
I don't want to live in a country where slavery is required for people to barely survive. I'd like to be on the right side of history. And if part of the tech industry has to be gutted or burned down, so be it.
'moralising' is actually a pretty good answer. When it comes to certain actions like organ donations, we're utterly terrified of the idea that someone will feel like they 'have' to do it. Getting a million dollars, even though it would have an amazing impact on your life, is bad because you'd feel pressure toward doing it. Getting a small payment would also be bad because you're being taken advantage of. But you can do it for free if you so desire!