Steve,
The Watch Tower does have a defense in that it could pair the sex offender with another JW. But, I don't think it's a great defense. Here is why.
So much information is learned when the pair of JWs ring a doorbell. Does a dog, a big dog, bark? How long does it take to answer the door? Did the householder have to push buttons (alarms beep when they are turned on and off)? Are the doors locked? How many locks are on the door? Who answered the door? If a child, is the child alone? Is the child a latch key child, as so many children, tweens, and teenagers are? This is a wealth of information that a sex offender can gather, and then use at a separate time. Hence, the Night Stalker case that recently came out.
Let's say that a grown up accepts the literature and starts a Bible study. The grown up has children, which may be included in the study or may play in other rooms. Are the JWs going to stop a brother/sister from conducting the Bible study because they have a record, say an old one at that? Surely, they will permit it. After all, even elders can be reappointed as elders if they are "clean" for 3 years. We learned this from court paperwork filed in the California sexual abuse case. The householder is going to get very trustful of his/her study conductor. What if something happens to the kids? Is it truly a private matter between the householder and the study conductor - or was the whole thing, from the initial door-to-door call, to the at-home bible study arrangement, to the books they studied, to the elders allowing the sex offender to conduct the bible study (which is tracked in the monthly service reports)...all connected with the Watch Tower Society? I think the latter. There is trust on behalf of the Bible student and her family, and a law on the books that makes her believe that all ministers are checked.
Skeeter