I don't disagree with that, but then the risk is nuclear war. It could be triggered by global warming conflicts or by something else.

Still, like I said somewhere else, even all out nuclear war is unlikely to lead to human extinction. It could push us back to the neolithic in some scenarios, but even then there is some disagreement about what would happen.

Of course, even in the most optimistic scenario it would be really bad and we should do everything we can to avoid it - that goes without saying.