I agree, but I was also advised by a solicitor once to get 'evidence' of abuse happening, which would have meant putting the child in danger just to have the evidence. Better to have someone who is not a child go through that, than the actual child.
With paedophiles it's often people they are close to, so I think the vigilante approach works well.
Plus you often find they have friends or family who stand up for them (or are in denial), so having other people who are prepared to see what is happening and give support can really help.