The problem isn't that it's easier to destroy - it's that the amount of destruction that an individual person can wield is increasing at a much greater rate than the ability to defend against that is. Firearms are becoming more accurate and more destructive. If you went amok at your workplace before firearms, you'd probably be able to kill two or three others before somebody took you down. With guns, as the Columbine Highschool massacres showed, two people can take down a LOT of people. Then we've got 9/11 - people willing to trade their own lives took 3000 lives.

All it takes to set off a nuke is one person.

As technology advances, new "improved" ways of killing people at a distance, in larger numbers, will work their way down the chain. Fewer and fewer people will be required to do the killing.

That's the real issue we need to deal with, before we get to the point that somebody builds and uses a planetbuster.