The creditor failed that by not offering the credit at zero interest, as they would have liked to have done unto them. Why should the golden rule only be applied one way?

I don't understand your line of reasoning.

You are a lender of money. Someone asks you for money. What's the interest rate you should charge if you apply the golden rule? Zero, because that's what you would want to be charged. Therefore, the creditors in this case broke themselves the golden rule, and shouldn't complain that the debtors did also.

Why would I want the lender to charge me zero interest? I know that she can't do that, particularly if I know I'm a risky borrower.

I want a rate that is reasonable to the risk, because if I insist on a lower rate, I won't be able to borrow at all.

I think you are knocking down a straw man argument; namely that "the golden rule means 'give away everything you own'".

I don't think anybody who would use the golden rule as a moral tool would really interpret it that way.

Not give away; I still wrote "lend".