What it is
Real food with a defense system: oxalates, the plant's mineral-binding deterrent.
Why your biology objects
Oxalates bind calcium and iron on the way through and, in stone-formers, can crystallize in the kidneys. The ancestral fix is built in: boiling pulls 30–60% of the soluble oxalate out, and eating these with dairy binds the rest in the bowl instead of in you. Your ancestors cooked their greens.