I thank Vladimir Putin for reminding everyone of the original purpose of the North Atlantic Treaty Organization, and the value it still holds.
This is one of those classic international relations dilemmas where it's unclear what Putin's intentions are so it's hard to read the situation. If he just wants to formally annex Crimea and keep Ukraine from joining NATO as you noted it could ultimately end up making NATO stronger in the region and put Russia in a worse geopolitical situation even with Ukraine out of NATO. But some people think his goal is to discredit the entire NATO alliance, in which case he's going to keep stepping over the line until he forces a confrontation, hoping that NATO and especially the US will back down, proving the agreement to be a bluff. Hopefully that's not the case, because it could put everyone in a very dangerous situation.