duh i guess we are all so stoopid.....we all (like our marxist prez) better listen to Medvedev telling us what we should do.....
gosh now....we wouldn't want that would we.......?
Medvedev is not telling us what to do. He's stating his country's concerns, which happen to perfectly valid. And no, we don't really have an incentive to undermine Russia's nuclear deterrent. Having that ability is only important if you seriously think Russia is going to launch a first strike, which doesn't make any sense whatsoever.
Since it is extremely unlikely that the United States would launch a first strike against the Russians, there is no reason for the Russians to be concerned that a missile defense would be a problem for them. I imagine that you would agree that the United States can also have valid concerns about missiles from Iran, and the number of interceptors necessary for that defense would have little impact on a Russian nuclear deterrent.
We absolutely have valid concerns about Iran's weapons development. Those concerns don't require placing missiles in Poland. Your point is valid that Russia doesn't need to fear a first strike from our end, but that's like me shaking a loaded gun in your face while promising to not shoot. It doesn't matter that I've promised not to, the big loaded gun is scared nonetheless.