As long as nations consent to being protected by a missile defense shield, it is consistent with national sovereignty. Anything that can protect a country from potential disasters should be welcome. There is no good reason to oppose defensive measure to protect a nation's citizens. Missile defence would benefit any country.
European missile defense is consistent with national sovereignty. Although Europeans are somewhat skeptical of missile defense because of their history of letting allies tell them what to do, it is still Europe's decisions whether or not to accept help. Europeans are not used to having a lot of decision making power when it comes to security measures, but they must embrace it to maintain sovereignty.