Anxiety over crypto-converts shifted Spanish prejudice from religion to race

Evidence

As noted, determining who was a crypto–Muslim or crypto–Jew after conversion was one of the central preoccupations of Catholic Spain, and the anxiety it produced created tremendous animosity against Muslims and Jews and against former practitioners of these faiths. That fear was an important feature in the transition from religious conceptualizations to racial ones. — Junaid Rana, Terrifying Muslims, 179

Categorization

• QUESTION: Worth investigating: how exactly did the impossibility of verifying true conversion mechanize the slide from religious to racial categories?