I realized that I am kinda judging the sanity of the author by how much I agree with her.

That doesn't seem horrible to me. There are many ways of being insane, but one of them is having a very wrong map (and you can express the one of standard criteria for clinical-grade mental illness -- interferes with functioning in normal life -- as "your map is so wrong you can't traverse the territory well").

I think the critical difference here is whether you disagree about facts (which are, hopefully, empirically observable and statements about them falsifiable) or whether you disagree about values, opinions, and forecasts. Major disagreement about facts is a good reason to doubt someone's sanity, but about values and predictions is not.