That wouldn't happen. As I said, I'm not going to let people train if that's their MO. If a parent was concerned about the type of person rather than a specific incident, then I would tell them they should look for another gym for their kid. I've never regretted losing money for something I believe in.
And to answer your question directly, I am willing to risk the very very small chance of that kind of activity slipping by me in order to build an inclusive team.
You're from NZ, right? What experience have you had that gives you your perspective? I ask because all my experience, personally and professionally, is that these 'shady' people are training to improve their lives and get some positive direction, not use the gym as a recruiting ground.