You are right -- our country is in no position to trifle with Russia right now (which is kind of sad if you really think about it). But, to be honest, with the way jingoist sentiments are growing across that country, I can't help but wonder if the current situation in Ukraine is a window we might later regret not fully opening. It's not a decision-making process that I envy in the slightest but, at the same time, my confidence in the Obama administration to handle this (mainly due to a lack of credible diplomats) is minimal. This would've been a great moment to test Hillary Clinton's mettle as SoS.
Also, I wouldn't be so sure that our Western allies will turn a blind eye to what's going on. Instability in the Ukraine directly effects several fledgling EU member states.