A missile defense system for Europe, in my opinion, is an absolute no-brainer. Between dealing with the Russians, who are slowly returning to their old Soviet ways, and the threat coming out of the Islamic Middle East, especially an almost nuclear armed Iran, not having a missile defense system would be foolish. The only argument against it is that it would upset the poor little Russian government.
A missile defense system is superfluous--the nuclear age is over and Russia, while hotheaded and hardline, won't do anything stupid as was thought during the Cold War. Good diplomatic relations with everyone promotes peace and naturally increases security between nations. There is no substitute for good relations in peacetime in order to bolster secure ties with other countries.