I read a thing recently that argued that "purity" is one of the most distinctive thematic motifs in fascistic thinking, and examined how that is a means by which people can slide into right wing ideologies from an initially left wing position.

It was striking because it made it clock for me why there seems to be a "crunchy eco-leftist turns right wing" pipeline. To attempt to summarise some of the article and my own thoughts following it: A purity oriented framework of health situates "toxins" and the like as the Big Bad Other. Many of us are aware of how dangerous the notion of a Big Bad Other is if we're thinking about people, but it can creep up with us in contexts like this because it doesn't seem harmful initially. However, by thinking about health in this way, we train ourselves to think in terms of the Big Bad Other, and condition ourselves towards thinking about things in a black and white manner.