When the U.S. claims the right to invade any country unilaterally and then defines a country like Iran or North Korea as "evil," then it is a rational response for these countries to develop nuclear weapons as the only military deterrent to invasion. We create what we most fear.
The nuclear genie is already out of the bottle, which is terrifying. Pakistan already has nuclear weapons. Since the Dept. of Homeland Security report ("U.S. Report Lists Possibilities for Terrorist Attacks and Likely Toll" by Eric Lipton, The New York Times, March 16, 2005) indicates that there is no way to eliminate the risk of one or two people detonating a small nuclear bomb in New York and/or in Washington DC that could kill millions and cost billions, perhaps our security may be increased by acting in ways that cause the rest of the world to love us rather than to fear us.