It is undoubtedly a better thing to actually defend your populace than to hold the men, women of children of your adversary hostage to against the behavior of their government. But as a practical matter, none of the ABM proposals and programs ever came close to the ability to make a full on attack by the Soviet Union “survivable” enough that it wouldn’t deter the US from actions likely to trigger one. During most of the cold war, the rule of thumb was that crossing the Iron Curtain with troops in Europe by either side would lead to nuclear war. Proxy fights in the rest of the world, wouldn’t*. When the Soviets used military force in Hungary and Czechoslovakia, the West did nothing really to stop them.