I'm actually in support of this. You can argue about the extent of the deployment, but when you play Realpolitik, you have to play.
And Russians being Russians, they will only stop when they think you are serious about stopping them. If you doubt this, ask the Georgians, the Ukrainians, or the Chechens. Or the Poles, who know all about Russians, and are ecstatic over our arrival.
Plus, Poland is a NATO nation, and we are well within our rights to post troops wherever we damn well please. Russia isn't going to start a war over this, but they may begin to cool their jets on bullying their Baltic neighbors.
This is one of the few times I'm agreeing with Obama on something. Savor it.