It's not pragmatic to lose, for what it's worth. We know that reform is impossible, and Bernie likely knows too. You're correct that had the Democrats run on a progressive anti-genocide Social Democratic platform, they would have won, but that's not what their donors want and need.
Marxism is vindicated by the passage of time.
The problem is that because voting is easy and low risk, it doesn't actually go far enough to get change. The dems are not an anti-fascist party. Capitalism is in constant decay, this decay leads to sharpening contradictions and fascism is deployed to protect Capitalist interests. Bernie would not end Capitalism, he may only slow it's rate of descent, not stop it or reverse it. A great work on fascism is Blackshirts and Reds. I can provide a longer Marxism intro reading list if you'd like, but Blackshirts is a great start.
I understand your fear, but we can know the enemy, why it rises in strength, and can banish it forever.