Nor is there any purpose to be gained by saying Ukraine should strike Russia. It makes an increasingly "threatened" regime even more nervous.
To be fair, the Defence Secretary didn't say that Ukraine should or should not strike any particular target. What he said was that a strike against Russian military targets would be legitimate, even if those targets were on the other side of the border.
I think many people don't get the fact that nuclear war is an extinction event. There is by definition nothing worse than it.
It is not. First off, there is such a thing (in theory at least) as a limited nuclear war. A few tactical nukes dropped on the battlefield will be locally catastrophic, but globally a non-issue. Ironically it might actually help with climate change by providing a degree or two of cooling for a short period.
Even all out thermonuclear war would result in the end of the current civilisation, but would be highly unlikely to result in the extinction of the human species. Globally the death toll would be in the high tens to low hundreds of millions in the active phase of the war, and over the course of the decade that follows you could probably expect somewhere between 0.5 and 2 billion people to die of starvation. It would likely set humanity back to a level of technology that wouldn't be far out of place in the late middle ages.
Recovery from the conflict would be likely to take somewhere between 50 and 100 years. It would be bad, yes. But it wouldn't be the end of humanity.
Allegedly none since the treaty in 1990 but I wouldn't be surprised if there had been. To be fair that's 30 years ago...
It's impossible to test a nuke in secret. I mean, even the Buncefield oil depot explosions triggered nuke detector seismographs in America.