Good gardaí let themselves down by not pointing out rotten apples
By endless trawling through records, and more detailed investigation when necessary, they help to ensure that people with any sort of established history that would make them dangerous to children are less likely to get through the net.
The system is by no means perfect. It needs more resources and better access to overseas information. And even if it were much better resourced, vetting alone is never an ultimate guarantee that people who want to prey on children can be prevented from doing so.