But MAD is still what keeps the world relatively peaceful. It also gives rise to certain paradoxes - like any attempt to create a better defense against nuclear weapons is also the biggest threat to mankind, because it risks breaking the MAD doctrine and thus inviting a nuclear first strike. For MAD to work, countries in their equivalence class (e.g. US, Russia and China are one class) need to be in lock step with their capabilities, so that no one can be struck without the attacker risking annihilation.
There seems a kind of anthropic principle here - it seems successful, but we wouldn't be here talking about it if it had gone terribly wrong, which has come very close to happening more than a few times, apparently.
The risk of that is >0, but the cost is...infinite. That doesn't seem obviously worth the gamble, to say the least.
I just don't buy the apparent absolute certainty it won't kill everyone. Then anything else would have been preferable to the "stable equilibrium" we were assured was necessary. But we won't be around to talk about it. That eternally living under MAD is 'the only way' seems to me more like a religious belief than a realization of a fact. A uniquely insane/evil one, however you want to describe killing everyone on Earth. Perhaps it's not considered so evil or insane to do that if you meant well?
It is the presumptive fact in the absence of viable alternatives. IF one is discovered, we can revisit the question.
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.
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.
It's a tough goal - perhaps the hardest there has ever been - but it's not impossible.
A world peace might be plausible through a single world government that can enforce a world peace and resolution of diverging interests and conflicts without war, i.e. with some "policing" mechanism instead of relying on people not escalating through sheer goodwill. That is possible - world peace based on the expectation that any potential violators of that world peace would face retaliation and lose in that conflict. Si vis pacem, para bellum - that can work, if it can be established.
Or, alternatively, a world peace through mutual respect and tolerance may happen if at some time in future our civilization consists of substantially altered individuals - genetic alteration, chemical brainwashing, computerized circuits in brains, something that changes the way our motivation works on a fundamental level - but not for people as we are.
Otherwise, as long as any people and groups of people have unmet desires (not merely needs) and diverging interests, conflicts will happen, and as long as violence is a practical option for achieving goals (i.e. there's not a threat/expectation of successful powerful resistance to that violence) it will be considered and used if mere threat of that violence isn't sufficient.
I get the feeling that's not generally known. Isn't that kind of extremely weird? I've never seen discussion of it on HN, for example, or maybe what to do about the prospect of living indefinitely under the threat of MAD. With more countries with nuclear weapons all the time. Well, you read here about people not wanting to have kids because of global warming, but not because of that. Is it just too big a problem to even think about?