They'd become martyrs.
We are talking about a religion that one of it's main tests of faith is persecution. They'd be examples of "being faithful till the end" in more new publications than you could shake a bookbag at.
Exactly. Imagine the effect of the "persecution." They'd have something which would make the national, maybe even world, news circuit and put the witnesses in the forefront of people's minds. The witnesses are really a low-profile religion regardless of how their members think of themselves. A lot of people generally dismiss them as irrelevant. But if someone were to go in and wipe out the entire GB, that would change over night. The witnesses would use that as proof that they have the truth. "Satan targetted us in a big way. What other religion has something like this happened to? See? We have the truth!" It would do more harm than good, and I use the term "good" in a lose way. The taking of a human life is not something to be viewed as "good."