As someone who knows as excessive amount about actual public policy, admittedly a statement you can’t really confirm, let’s focus on some of policy that Bernie ignored.
What about the goal of a more open society. This is something that Bernie rejected. He rejected this through his disdain for trade. You can call me a neoliberal all the you want, I don’t care. I am willing to accept that label as it’s so called neoliberalism that has brought us the modern world. A more open economy helps the world as a whole. If you’re trading with someone, you probably won’t go to war with them. It also helps people empathize with people in other countries. An ability that I believe would have drastically changed the outcome of the election. Bernie wanted to turn back the clocks as Trump does, but he just wanted to do it without the racism.
Your winnow out statement is simply denying reality. Who got more votes in the primary? Here’s a hint, it wasn’t Bernie. This shows the relatively narrow appeal of his exceptionally limited vision. Yes, he did have a vision, but was simply lacking knowledge and policy in a large number of areas (see inequality outside of poor white problems and foreign policy).
Suppose you were able to winnow out such individuals (a big hypothetical), where would they go? Would such individuals not form a new centrist parties with the tentative/centrist republicans. Would such a part not defeat the hollowed out democratic party?