Would you use the same isolationist argument if he now takes the rest of Ukraine? Belarus? Georgia, Khazakstan? Those are relatively disfunctional goverments as well.
I have always been a super hawk.
I have always been a super hawk on defending our friends, like Israel, Kuwait, and Taiwan.
And, in years past, on defending western Europe, South Korea, South Vietnam, and Japan.
I lived through the most dangerous years of the Cold War, including the Berlin Wall, and the Cuban missile crisis, where I had a front row seat from south Florida.
To this day, I believe John Kennedy was a weakling who caused both those crises.
Crimea is different.
A majority of people living in Crimea do not want to be an ethnic minority ruled by a chaotic, authoritarian Ukraine government.
A majority of Crimeans do not want to live and work in Ukraine's train wreck economy.
As to Putin, the man has no moral compass, but he does have political common sense.
He would need to re-establish a violent police state to control the old territories of the Soviet Union.
Is he capable of doing that?
Sure.
Will he do that?
I will need to see a lot more evidence then I have seen so far.
For instance, if Putin threatens the Baltic countries like Latvia and Lithuania, then, yes, I'm on your side, and we should definitely risk military action.