Party loyalism requires selective ignorance.

Having been raised on the right then switching to a more left-center view, I don't see how it's demonizing. The right of my youth and today idolize some imagined past that never existed and fixates on threats to reaching that ideal. 'Good' changes are almost always a return to something old and 'trustworthy'.

Occasionally the left does get stuck on defeating some right-wing figure, settling for mediocre or even poorly suited candidates (cough Biden cough). Though more often I read/hear more about changes toward progressive goals than fear mongering.