Thats assuming you think that the reasoning for this is actually due to the apparent "threat" of NATO.
It makes no sense to me to consider this as the real reasoning. If Putin wants to stop or reduce the amount of NATO troops and weaponry on his border, then invading another country will not do that, in fact it will do the total opposite. The amount of permanent NATO troops in Estonia, Lithuania, Latvia, Poland, Romania etc will rise dramatically.
Now you can look at this in 2 ways. Putin is an idiot, and doesn't think the above will happen. For me, I don't believe that, Putin doesn't strike me as an idiot.
So logic tells you, that the above IS NOT the reason for the invasion but is being used as propaganda for the invasion.
Putin has said on numerous occasions about historical Russian borders, he barely recognises that Ukraine should have autonomy from Russia. I believe that the base of this invasion (as poorly thought out as that is) is that I believe this has imperialism at the heart of the decision.
You can try and put words in my mouth and assume I haven't looked at it from Russias POV, but I have. I just don't believe the whole story about this being done to stop and reduce NATO's military influence in Eastern Europe, as this action will only have the impact that it has the opposite affect to what Putin wants.