Then the Soviets start with the argument that they were being defensive about a western front invasion from Germany - which, after 1813, 1914, and 1919, was not without precedent. So we have now two aggressors claiming defense. Someone is bullshitting but their arguments are indistinguishable.
That's the whole problem: if you're paranoid enough about what might maybe happen someday, even if entirely unprovable, you can justify any act of aggression no matter how aggressive as defensive.
Don't accept it. Don't let it have any kind of basis. Don't let that argument be made. Don't even let that argument begin. Be clear on who gets to claim defense.