I don't think your analogy is particularly accurate.
If I was to sell one of my organs, it would A. have an immediate detrimental effect on my health and B. be permanent. Further, the state has a very high probability of paying for some or all of my medical care post-op.
If I sell a baby, I am selling something that is not my property. If I am the parent, I have some claim to the baby, but not one of direct ownership. So in truth I am selling something that is not mine. In reality, what you would be selling is your lack of action in defense of your paternal rights. That is, in fact, a victimless crime. However, the administration of those rights is not yours alone, but also your community's. You can't sell that, so you'd be lying to whoever you gave the child to if you implied that you could.
Lots of decisions and transactions are only technically voluntary and are driven by economic duress more than anything else. Working a dead end job, working a dangerous job, being a roofer or garbage man or flagger. Joining the military. Being a lumberjack. Hell, being a fisherman in many cases.
A lot of these jobs are dangerous. They're accepted, though. If I work as a lumberjack, it's not because I have a choice. It's because otherwise I would be homeless and this is a skill I can employ to feed and house myself.