military brass often take the security dilemma even more seriously by thinking ahead of the politically foreseable future into geographical imperatives.

A = Russia's mindset for centuries has been to have a large buffer because the plains are hard to defend.

B = Now suppose for the sake of argument, as premises, that NATO is 100% defensive and so russophile that there is 0% chance that anything bad to russia happens in the foreseable future given current leaders and politics.

A + B => fine, but if UA is in NATO, how would russia be sure these premises would hold 30 or 50 years in the future? They have to stop it now, anyway, to avoid a future existential threat. They said repeteadly that UA in NATO would be a red line. Right or wrong, they see it as a threat, with some reason.