I would suggest as a first step, if one takes part in the system, that one at least get a commitment from the United States that it's part of the NORAD construct. Once that occurs, then it necessarily becomes an obligation for the command to defend the continent binationally. Therefore if we can arrive at a political agreement, and that would be a diplomatic agreement, then NORAD would be duty bound as a binational command to protect the continent equally, as opposed to focusing on some areas versus others.
On the other aspect of your question, diplomatically I think it's important to note we are effectively committed, except in terms of having the system defend us. So we have stated as part of our alliance in NATO that we support the system. That for me is the odd part, in that in the past we were militarily committed but diplomatically opposed. Now we're diplomatically supportive, but militarily opposed. So it's a strange situation that we find ourselves in, and it's simply to encourage us to have the courage of our convictions. If we truly believe that it's a destabilizing system in international affairs, then the question behooves us, I would suggest, to try to get our other NATO allies to reconsider as opposed to signing on without saying much about it.