Supreme Court says otherwise, if you're a cop.
Heien was about meeting 4th Amendment probable cause standards to prosecute a different crime. This is about ticketing people over the non-criminal act out of ignorance. It's like if Heien had been fined over the brake lights even though they were legal.
As is, the NYC statue of limitations will strip most of these people of the right to contest tickets that were given for non-crimes.
However, in this case, returning the money with interest would be somewhat punitive, and that would indeed be appropriate, as it would discourage future carelessness in enforcement and abuse of the citizens of NY.
If you fail to pay all the taxes you owe, you are required to pay penalties. If the government fails to correctly enforce the law and wrongfully fines innocent citizens, why should it not be required to pay penalties?
This is the most basic way to hold government accountable for such carelessness. When a department fails to meet its budget because it did not correctly train its officers in the law, did not properly oversee enforcement, and now has to repay what it wrongfully took, those responsible for the oversight will be replaced with others more competent. As a result, the citizens have a more competent, ethical, accountable, and efficient government.
Wherever did you get the idea that, "Well, as long as you promise not to do it again..." is a sensible solution?
In an argument where the authorities are using the cost of repayment as an "argument" -- that's pretty silly.
There's been a huge proliferation of laws in the last ~20 years or so which are categorized as Strict Liability. Taxes have always been like this, but lately a lot of new laws have said "follow this or else" full stop.
Since normal everyday citizens are being held to strict liability every day, I see no reason to be so forgiving of officers. I'm not suggesting that they're bad people, or deserve to go to jail for making an honest mistake. But what's good for the goose is good for the gander and if normal folks are being punished this way, so should law enforcement, politicians, etc. Nobody should be exempt, the law is the law.
https://en.wikipedia.org/wiki/Strict_liability_(criminal)