I totally agree with what you say....but I think the slight failing of it is "any reasonable person".On the one hand I get this paranoia for historical reasons, but it isn’t founded in logic or common sense.
Firstly, because none of these invading forces have succeeded.
Secondly, because the nature of warfare has changed. Invasions are much less likely to succeed than in the past. Guerrilla tactics, communications technology, the widespread ability to make explosives and now the rise of relatively cheap, widely available drones means it is much harder (and much more attritional) to hold territory you have claimed. Afghanistan (on numerous occasions) Iraq and now Ukraine have suitably demonstrated this.
The notion that NATO would invade Russia is so preposterous that only someone utterly deluded would actually believe it. It would be an insane undertaking that would be doomed to failure. And to what end?
It’s easy to blame this Russian viewpoint on state propaganda, but any reasonable person applying their mind to it must surely see it is a complete fantasy.
Decades of state media, schooling, stories from parents and grandparents will have indoctrinated the population (abit like reading the Echo) to believe that the government knows best and is protecting you from those horrible decadent westerners.
There is also the thought that some people, the word that first came to my mind was "deplorables", need something to rail against or believe in. I wonder how many of the US population supporting Trump, "the steal" & Fox News see themselves as any different from Putin supporters.
A belief that if you dont support the media/government view, that the bogeyman will be coming to kill you and all your family, does impact on how "reasonable" some people are.
The scary thing is that Russia has been a dictatorship for years so there is perhaps some excuse, whereas in a democratic country like the US it does cause you to question some peoples sanity.