Maybe MPs don't need to be vetted because nobody trusts them. Even kids can see through them.
On the other hand, a spokesman said the other day, that even if authors are infrequent visitors they should be vetted because they might (by chance) meet children who trsut them, outside of the school environment. Well, duh, so might anybody else. If we are worried about kids bumping into people they trust, maybe all TV presenters, actors, musicians, etc should be vetted as well. When I was at school we spent as much time in the local sweet shop as we did in any of our classes. So all the local shopkeepers should be vetted as well. And the bus drivers. And parents. And siblings. And those doing the vetting. And vets. And....
So why not put the entire population, apart form the MPs of course, on the sex offenders register, tag them all and give them a curfew. Job done.