"I dont see why they cant be expected to say no. I mean they could couldn't they? That's not to say councils and libraries aren't responsible for poor choices and irresponsible actions but I dont think that means we shouldn't be able to expect a person to do the right thing."
It's paid work, it's in their area of work and it means they are doing their act rather than their survival job. If the job is offered, a lot of performers will take it. The recent problems have been when the performer didn't have child-friendly costumes, or didn't re-write the act enough. In both those cases, it could be argued that the performer didn't realise there could be a problem.
Actors and performers often have to do things for work like strip naked, simulate sex, or undress very quickly in an area where people of both sexes will be rushing around. Do that long enough and our sense of 'what's appropriate' will become a bit blurred. There's a reason child actors must always have a parent or chaperone in attendance when not actually on stage.