I’m not sure why I find this disturbing – I think the idea that some of these vigilantes are getting some kind of kick out of pretending to be 14 year old girls is probably one of the major factors. In this context, this kind of activity is entrapment, it should in itself be illegal.
There are, obviously, problems that need to be solved here, one of the major ones is the abdication of responsibility by parents, externalisation of the problem – “The internet exposed my innocent child to danger” instead of “My child knows not to talk to strangers”.
The world is a dangerous place. Sorry, you just have to deal with that.