My argument would be: we should have worked harder to make the rules good in the first place. Yes, I agree that damage to the credibility of the system is bad,

My argument would be: we should have worked harder to make the rules good in the first place. Yes, I agree that damage to the credibility of the system is bad, but it can easily be the lesser of two evils. We have release valves like bankruptcy for a reason - we don't want to get stuck in negative feedback loops. See the current trend towards nullifying possession charges for Marijuana. Yes, it sucks for people who got punished under the old rules, and yes, it's not good to say "laws might change and you might 'get away with it'", but sometimes that is better than letting a lot of people suffer.