I actually had a discussion with my Dad (who was an MS) back in 2009-2010 about known pedophiles in the congregation being allowed to remain JWs and go door-to-door.
In my province of Ontario, Canada, a child as young as 10 years old can be left alone at home legally for about 1 to 2 hours as long as they are mature enough to handle it. This means children will be alone at home and these predators are going to knock.
My Dad had no response to this. I don't think he had thought of it either but I could tell he was disturbed by it.