People doing illegal stuff will use whatever means they can get their hands on to do their illegal stuff. Giving them an easy to find platform means more illegal stuff is done, not less so adding a barrier will cut down the amount of abuse at the expense of making it harder to track them down.
It's a tough choice but rewarding the enabling of crimes like these is entirely the wrong signal, it makes it seem as if this is normal and acceptable which it never should be.
The other side of the coin is that the operators probably already use multiple sources for their 'customers' (I use the word loosely, you might as well read co-criminals for it), and that shutting this one down will only cut off a portion of the hydra that has visibility in the otherwise respectable part of the world. Punishing the customers of child prostitution while at the same time legalizing the regular form goes another step in the right direction, but may not be acceptable in all political climates.
