The Soviets were parking nukes in Cuba in striking distance of the White House. If that's not legitimately terrifying to you, I just don't know.

Not anymore than the US being able to strike worldwide to this very moment. They are the only country that has used nuclear bombs against civilians.

The big problem is having one country be able to do it without deterrents and with impunity. MAD is a good thing, if anyone will have those things at all.