We need a healthy Russian economy
Big, powerfull countries in utter economic ruin are extremely dangerous. Look at Germany between the wars. Add huge nuke stockpiles that are the only military force the country can afford, and, well, consider the idea of Hitler (I'm not thinking of Russia's current leadership, I'm thinking of what, under continued economic ruin, the replacement might be) with a few thousand nukes sitting around.
For a variety of ugly political reasons on both sides, there isn't much we can do to improve the Russian economy. But if we get another arms race going, we can make it worse. Bad as it is, there is still room for it to get worse.
It would be nice to get past "duck and cover". But that isn't what the missile defense system is about. The missile defense system is theoreticaly about preserving our retaliatory strike capability. But there are so few scenarios where it would be relevant (Iraq would use ground transport or aircraft, Russia or China would simply overwhelm the system by launching lots of missiles, it might protect us from France if the positioning is right) that I have to suspect that the real purpose is either to transfer funds or to help future Texan schoolchildren confuse George II with Reagan. Unfortunately, when Reagan did it, damaging the Russian economy was in our best interests. And that is no longer the case.
