It's simple:
- NATO is the aggressor by virtue of (*checks notes*) forming alliances in the vicinity of a country with a century-long habit of biting chunks out of Europe.
- The forming of alliances by NATO within 1,000 miles of the Russian border therefore justifies any and all action (military or otherwise) by Russia, and any and all resulting death, destruction, and seizure, occupation, or conquest of land.
- The West has failed to learn the most important lesson: if you don't want Russia to invade you, don't form relationships based on Russia's repeatedly demonstrated fondness for invasion (the West has been wearing a very short skirt for quite some time and was clearly asking for it).