Yes, a European missile defense system is effective, because it prevents other nations from attacking Europe. Other nations will be less likely to attack Europe if they know that it will not be effective. This is a way of effectuating Reagan's principles of peace through strength. A missile defense system allows Europe to show strength, which is effective.
The Missil defense system is effective because it is a program put in place to protect the European warheads. Any defense system in place means that there is most likely offensive international adversaries such as terrorists who could be approaching the country land. A missile defense system is much needed.