I suspect that this is not due to there being anything morally wrong with what they are doing but that instead of going after the perpetrators, which might be very difficult, we target the economy which pushes them to commit the crimes in the first place. Although it might be imperfect, from what I understand sometimes this is the best way to get results.

In a way it's similar to prostitution, where there might be nothing morally wrong with selling or buying sex, but it (potentially?) promotes human trafficking. I doubt that'd the only reason it's illegal though, at least in the US.