The implicit promise was "I will act lawfully, which means that I will do my best to repay; however, if I find I am unable to repay, I will lawfully use the leg

The implicit promise was "I will act lawfully, which means that I will do my best to repay; however, if I find I am unable to repay, I will lawfully use the legal recourse for this situation, bankruptcy". It was not broken. One can't just declare themselves bankrupt - you have to go through the legal system to do that, which supposedly verifies that you indeed qualify for the protections afforded by bankruptcy. Note that this is the same legal system that enforces the lender's rights in case you are able to repay but will not.