From July 1945 through the early 1960s, the US detonated hundreds of nuclear weapons on the ground, on the sea, in the air, and even a few in space. Starting in 1949, the Soviet Union did the same. These included some monster bombs with yields in the 20+ megaton range, far larger than anything in our current inventory. In all, there were well over 1000 of these above ground tests. Not to say these were benign, but the human race managed to survive all of that fallout.

The idea of developing updated ground penetrating nuclear weapons has been around for several years. There are some targets that couldn't be taken out any other way. One legitimate concern has always been that "cleaner" bombs that produce less fallout and surface blast effects might lower the resistance to using nukes.

Nuclear weapons seem more useful from a political than military perspective. If one side has them and the other doesn't, it becomes easier to force the weaker side to back down. If both sides have nuclear weapons, like India and Pakistan, then both have reason to fear the effects. As insane as it sounds, Mutual Assured Destruction (MAD, the most appropriate acronym ever), actually works. Militarily, both sides having nuclear weapons means the likelihood of a massed invasion (such as D-Day) is lower because a single weapon could take out thousands of the invading force.

Consider the case of North Korea. Their economy is a basket case. They have very powerful conventional military forces, but how long they can sustain them is questionable. However, possession of even a handful of nuclear weapons and the means to deliver them makes them a force to be taken seriously. A few years ago, they tested a missile that could have the range to reach Alaska or Hawaii. They're working on longer range versions of the missile. Suppose they said, "We're taking South Korea, and if you try to stop us, we'll destroy Honolulu." Of course, we have the ability to hit back hundreds of times over, but what about risking several hundred thousand American lives to the threat? This is called Nuclear Blackmail. It's perhaps the sole legitimate reason I see to developing a limited missile defense system.