I think the basic problem with the claims that good missile defence would be destabilising is advent of rogue countries that have access to long range ballistic

I think the basic problem with the claims that good missile defence would be destabilising is advent of rogue countries that have access to long range ballistic missiles and to nuclear weapons. I simply can't understand how anybody could defend that it is actually good thing for North Korea to be able to send a rocket to Seoul, Tokyo or Los Angeles. If you keep defending game theory and mutually assured destruction, the real solution would not be to freeze the technological race but keep that race up, keep everybody unsure about progress of everybody else and keep only the largest powers actually on top of the race and the smaller ones being unable to pose harm. Because if you freeze capabilities you give smaller nations time to catch up. This creates situation with lots of players with parity (in this case ability to seriously harm everybody else). When the number of real contestants is low, the whole problem becomes a bit less complex and easier to prevent a real disaster. The proper behaviour (if we go with MAD) right now would be to keep developing missile defense systems. Because this would force others to develop new, more advanced, more costly missile systems. Which would cut off small players like North Korea or Pakistan from posing much threat.