I don't think NATO-expansion argument is propaganda, but I do agree that that's not the reason for Russia's actions.
That's mostly because in terms of NATO war isn't allowed, thus generally speaking there's isn't a lot of reason to be scared of the huge army that NATO represents.
What's really annoying to me as a coder and gamer is that, strategically speaking what Russia did was logical and expected. I'm speaking from a point of view of if this was StarCraft, EU4, CK2 or Civ5. And from that point of view, my biased monkey brain is telling me that if US left the EU alone, there wouldn't be a possible WW3 brewing...
Mildly interesting note, my father is studying Multinational law thing and we were talking about the role of NATO, the function it serves. We got to that topic because my argument was that my country (Slovenia) should either stop having a military or focus on having few but very specialised units, because as it is now, it's mostly just a waste of money, that's because we've got a population of ~2 million and about ~4-7k military units, depending on how you count them. Regardless, it's a number that compared to other countries is not even note worthy. Which is why my argument was that our military in its current state is a waste of money. BUT because we're so small we don't really have air forces, which is where NATO comes in. Because we don't have air forces our air is protected by currently Hungarian forces and the ones from Italy a few years ago.
What I was trying to find out with the conversation with my father was, if there's a way to gain the protection of NATO without having an army. But sadly that's not possible, because too be in the NATO, you have to have an army... There also UN which could protect you, but there response isn't guarantied and the response time is much longer then NATO. Thus ima way you're kinda forced to have an army...
I would still prefer removing our army, I mean... We've got pretty lakes and nice mountains, also good wine, why would anyone want to attack us? :D