Joel. I'd be fine with this if it was always transparent who made a mistake. However, courts cannot figure this out in most cases. Thus you make simple, predictable rules that assign responsibility independent of who is at fault. That is what civil law should be about (I think).

In other cases, courts can figure out who made a mistake. Then the court can assign blame. That is what criminal law should be about (I think).

In clear-cut cases you assign blame, in vague cases you default to simple, predicatable rules.

The simple predictable rule here is that the debtor is always responsible for his debt (at least before bankruptcy law)