I wonder why humans naturally tend to gravitate toward purity tests? I even have that tendency, though I try to suppress it whenever I notice it (not always successfully).

I’d guess it has a lot to do with in-group bonding being extremely important throughout our evolutionary history, and believing something hindering or just plain wrong is a very costly signal of loyalty, thus hard to fake — similar to flat-earthers and what they believe, or feminists convinced of the ubiquity and reach of BernieBros.