The gaping flaw in that argument, is that if Russia were that terrified of Ukraine joining NATO then they would have invaded back in 2008 when Ukraine and NATO began the membership process (like they did to Georgia). Granted Russia were worse off than they are now militarily but so were Ukraine, and even more so. It would have been a much better time to strike, but they didn't, they sat back and did nothing (except cheer when Ukraine chose to abandon it's NATO application a couple of years later, big mistake there) because their existential threat argument is just ******** they cooked up as another layer of justification for their land grab, it has no more validity than their argument that they're preventing genocide by Nazis.