I'd say it's generally known - everyone is aware of nukes and what nukes can do. The difference is they're considered much more of a known quantity these days: you can't use them, you don't use them, and you also can't fight a direct war with any country which has them. The idea of the "mad Russians" launching against the US has worn out, but watch what happens when you talk about Iran or North Korea having them.
What's more worrying is that most nuclear policy in the US was centered around condensing launch authority solely with the President of the United States - there's a heck of a lot of assumption that that person is a sane, rational elder statesmen type.
That MAD continues didn't seem that known on HN earlier today. (I didn't know it either.) When I wrote the GP comment, it had half a dozen sibling comments from different people, now all deleted, talking about MAD in the past tense, as a crazy thing that was believed in long ago.
the problem with MAD is it falls apart when you cross religious extremism with nuclear weapons. It's not rational to douse school girls in acid on their way to school but religious extremism turns it into reality.
The AD - Assured Destruction - part works just fine. Irrational actors don't assemble world ending arsenals (after all if you think you should rush to your death, why not launch when you have 1, given that you're most likely in a "use it or lose it" situation).
Even in your cited example - the people who do this sort of thing attack those who can't fight back. They are never in any danger of being immediately shot dead after.
While yes suicide bombers exist, this is more a question of arms proliferation and control then an indictment of the ineffectiveness of MAD or the general strategic reality of nuclear weapons. And the situations under which non-state actors have them are still a policing rather then political concern - North Korea or Iran leaking a bomb to another entity that then detonates it is the surest possible way that both those states will be dismantled by NATO, since MAD does apply there: proof that you represent an uncontrolled risk of nuclear attack invites conventional or nuclear annihilation, regardless of the mechanism. Civilian casualties go out the window when you have already suffered some.
What's more worrying is that most nuclear policy in the US was centered around condensing launch authority solely with the President of the United States - there's a heck of a lot of assumption that that person is a sane, rational elder statesmen type.