Quote Originally Posted by Big King Sanctaphrax
If you make it clear to the person you're performing surgery on you're not medically qualified, why should this be illegal?

Indeed, if all of the participants were willing it seems odd that they have committed any crime at all.
Because it sets a precedent that will inevitably lead to bad consequenses. Can't afford an artificial knee? I'll do it for $100! Oh and for the record, it's on your own risk.