This is what has happened although I'm not sure it has manifested in the way the author believes or wants. What the right has done, for example, is create supporters that irrationally attach their sense of being to them and deny or block out anything that goes against what they are told to believe. Both stories they present at the beginning can be true at the same time.

I don't think this is as crazy as it first looks. For instance our values are largely arbitrary. Perhaps you can justify them with rationality, but generally "don't hurt people unnecessarily" seems like something I'd expect most people to get on board with without justification, and is also something I'm 100% ok with being arbitrary.

But you need to be honest with yourself about why you believe what you believe about the world. We all have contradictory beliefs (and sometimes values), so it's only a matter of time before you catch yourself believing in stuff not rooted in your values. This could be harmless, or it could be destructive to yourself and the people around you, or it could allow people to have an unhealthy degree of control over you, your behavior, and how you perceive and interact with the world. All good advice still requires good faith interpretation, and some people aren't going to do that. How much are we supposed to concern ourselves with people who don't try to understand us?

And in general, I'm pretty damn skeptical of anyone who roots their identity in political alignment. Like I'm pretty firmly on "the left", but it's not like I walk around identifying as an anti-capitalist, which is such a broad and vague term I can't control how people perceive it even if some will take me in good faith. And that's still dozens of layers above the values that actually inform my political alignment, and there's a lot of bad-faith actors who appeal to political alignment to get you to work against your values basically in every aspect of society. It's still up to you to notice this and care.