I'm not surprised that the Russians are perturbed about Georgia wanting to join NATO.

How would the USA feel if Quebec left Canada, let's say, declared independence and stated its desire to join a re-established Warsaw Pact, allying itself with Russia?

Or what if Mexico did that? What then? What would the USA say about that?

Georgia borders on Russia. Don't forget that. Now put yourself in Russian shoes and imagine their strategic concerns.

They are playing normal great power politics.

The Georgians are playing normal small power politics and doing the standard thing when an enclave (large or small) decides to leave the nation and declare its independence. They're saying "You can't go, and we will happily kill you by the thousands to prevent you from doing so."

That's what the Serbs said to Kosovo, isn't it? That's what a central government usually says to separatists.