The question is not "Is it useful?" but "Is it useful enough to justify the risk?" In that case, the answer might well be yes, but there will probably be cases in the future where the knowledge is not worth the risk.
I agree that you have identified the right question. I disagree with you on when the balance shifts. In particular, I think you've picked a bad example of "dangerous" research, because I don't think the virus research you identified is a close question.
(That said, not my downvotes)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)