Honestly mate, I'm just tired.
I tried to explain that even people living contemporary lives can be completely out of touch with one another (it's why rich people become so unrelatable that we get memes about "how much can a banana cost, like $10") and so imagining what life was like 100 years ago, or 100 years from now, is for all intents and purposes impossible. You went off about understanding individual single differences, which totally misses the point: it's the confluence of those differences in their totality that constitutes an environment, and environments shape opinion.
I wasn't alive before Hitler. I can't imagine what it's like to not have a figure like him in my history, along with the collective lessons we took from two world wars. As a consequence of those wars, European war to me may as well be as far removed as the US civil war or the English Wars of the Roses, except for one thing: I got to speak to someone who lived it, briefly.
My brain can't really picture Europe at war (I've seen movies, but even modern combat movies aren't accurate and sell 1% of the reality). I've only ever seen peace, the longest peace Western Europe has known. That's my entire reality, and it's as different from my ancestors' as theirs was from anyone's before them: a completely different understanding of history and what that might mean next, and totally different access to information and to opposing ideas from people as far away as the other side of the planet. Fog of the future.. right? https://youtu.be/NVGuFdX5guE?t=166 Everything is obvious in hindsight.
Being called a nazi sympathiser for admitting I can't know this (by people who are certain they do) is what I find hard. If you're resolute that you're right, and that you needn't consider the totality of a situation before assuming someone's motives, then you can look coldly at what you believe and judge people on that one aspect alone.
It's a closed loop. If the challenging arguments are the ones you won't engage with, you'll never meet one that moves you.
I'd rather ask myself "what if I'm wrong" and see whether I can attack my own position... maybe the other person has context I don't, or paints a different picture with the same facts. That's usually the more interesting conversation.
Anyway. I'm sorry I called you names. I was trying to shame you into seeing it, which was never going to work and was wrong of me regardless.