Thanks for your question.
I'll first quickly glance over your examples;
Can mitochondria become cancerous?
Yes, it's hypothetical, but I think it is a potentially interesting question, as it has its foundations in the coupling of cell division and distribution of these mitochondria among the two daughter cells. I think it's a good question and I actually upvoted it.
Can GMO cause Mad Cow disease and wipe out humanity?
Heavily downvoted and closed in the meantime because primarily opinion-based, and I totally agree.
Is it theoretically possible to safely eliminate most viruses in the atmosphere, hence preemptively cure all the viral diseases?
Opinion based and I closed it as such, thanks for the pointer.
So I think overall such opinion based questions should be closed, but carefully, as there might be interesting questions hidden below the post. The mitochondrion question can simply be re-phrased as
Why do mitochondrial tumors not exist?
Or the likes and that is not a hypothetical question at all.