Ukraine, and Crimea specifically have value, and keeping them could look bad. I get it. But lets say you're Putin, and you hear the following:
"Hey, Putin, there's some serious s*** going on in the Ukraine. We've a great portion of our economy running out of one area. Should we do something?"
Do you:
A. Secure the entire country with a HUGE portion of the military
B. Secure the area your economy runs through
lol, I've already told you I probably would have done the same thing. But that does not make it legal. Or earn you many friends for that matter.
So much so that:
The remainder of Ukraine will be a long time foe now
Finland and Sweden, long time neutrals, are actively considering NATO membership now.
Poland, Czech Republic, Hungary, Bulgaria, Latvia, Estonia and Lithunia are all taking a much harder stance on NATO defence in regards to Russia.