The news from Crimea is unsettling, partly because it's not entirely clear to me whether it's bad to have Crimea reattached to Russia in some form.
From a utilitarian perspective, removing the most eastern-oriented portion of Ukraine from its electoral politics would pretty much guarantee a western-oriented political outcome. My less-certain idea is that Russians living closest to the rest of Europe may have more European attitudes, so moving this population into Russia might also somewhat liberalize Russian political attitudes.
From other ethical perspectives, this area was Russian and is populated primarily by Russian speakers, and was only transferred to the Ukraine recently (1954) by a Soviet dictator for reasons that have little to do with the historical or ethical way to govern the region. There are the Crimean Tatars, but AFAICT that's a relatively small minority. I think as a general rule the majority in a region does not have the ethical right to secede their region from the country, but that rule should have exceptions.
The key downside, which may be what motivates Putin as an upside, is that having a Russian-occupied region would make it very difficult for Ukraine to join NATO. This reason partly motivated the Georgia war. Still, I don't see what's to be done about it. The history of eastern Europe in the last generation has been a tremendous victory for liberalism. Consolidating these gains is more important and valuable than restarting a cold war.
Saber-rattling with Russia might have some limited value but not a whole lot, going beyond saber-rattling is definitely a bad idea, and Russia's status as semi-democratic/semi-dictatorial is still fluid, so there are opportunities for liberalization that shouldn't be discouraged. The end game here isn't Ukraine, it's the political liberalization and stabilization of Russia, and successful democracies on its borders take us in that direction.
The game changes if Russian invades other parts of Ukraine, let alone the entire country. That's a real war with assistance needed, although it also needs a limited scope.
One other point I saw somewhere - as in other parts of Slavic Europe, the division here may be more religious than linguistic, with Ukrainian Catholics oriented to the west and Orthodox to the east.