I'm not primarily suggesting intelligence as a factor. I'm saying that among those who might want to do something especially harmful to humanity, it is exceedingly uncommon to, for instance, go study specific aspects of biology that would allow engineering a plague, in a long and diligent fashion without revealing anything, and still want to do it afterwards; that takes "premeditated" to a whole new level. And conversely, the kinds of people who study those aspects of biology in a long and diligent fashion aren't especially likely to have the temperament to decide they want to create a plague.

It's not that it could never happen. It's that it is much less likely.

Thought experiment: suppose there exists some trivial activity that would end the world, using everyday household objects that is easy to enact but vanishingly unlikely to do by accident, such that it could only happen if you made a deliberate choice to do it. For the sake of an absurd-but-clear information-theoretically-unlikely example, "write this exact ten-word sentence on a piece of paper, and place it in the microwave along with a vinegar-soaked match".

Now suppose that activity becomes public knowledge. How many minutes does the world last? I'd bet against more than a day (if betting were of any use).

Making it simple and widely accessible to do such things is a bad idea.

> Your "Venn diagram" is wrong. People don't decide against crime because they are dumb, they don't do it because of legal repercussions.

That's a factor that shrinks the "people inclined" circle. It doesn't change the analysis they're making, or make the analysis wrong.