One question I haven't heard asked, and which was reminded to me by delft's link, is: what are the consequences of trying to sanction one of the biggest players in global politics?
Does the US no longer need Russian cooperation with regards to Syria, Iran and North Korea? What happens to their strategy of trying to play China and Russia against each other?
It seems to me that if the US were to push Russia too hard on Ukraine, they would lose big in other, more vital, areas of strategic interests.
And that, of course, is the real reason why you don't encroach on another power's core interests.
You are right to ask the question Solarz and I would say that the preparedness of the West to undertake such obvious risk gives an insight to what exactly is at stake in all this.
If The West has succeeded in inducting the Ukraine including Crimea into the EU and NATO, had succeeded in evicting the Russian Navy, taken over the facilities and turned the Black Sea into a NATO lake it would have achieved two very substantial objectives.
1) Remove the ability of Russia to project power beyond its periphery and lose its ability to support friends like Syria and Iran.
2) Suffer such a loss of national pride and confidence that the Russian state would risk face an existential threat from it.
It was a major and serious play and it is the kind of play that you do not get wrong because it is very difficult to go back from it.
So on the one hand, the West; you would suppose, would be best served by realising that the moment has passed and it did not get what it wants.
On the other though, it cannot afford to give up, as any pretence of reset, détente or perestroika have just been trampled into the mud.
This is why I see no option but for Russia to remove the Crimea from contention, as otherwise the efforts to loosen and destabilise will just go on and on.
For Russia and China, there is no longer any "polite" doubt about the West being trustworthy partners and future International relations will be carried out in that light.