Given that the risks to “creditors” (banks lending money back to people who own that money) are equal for debit and secured credit cards, and that the risks to “debtors” (people who would be using their checking account to build a neutral-at-worst credit history)…

Having the means to protect yourself is the baseline definition of a secured credit card. That’s why it’s secured. You’re starting with some positive balance and spending your own money. That’s what debit cards are too. The liberty banks take is choosing who gets to benefit from their normal spending of their own money being considered as credit at all.