>I doubt you're ambivalent about a behavior right until the moment it becomes illegal, after which you think it unethical.
There are many cases where I think that. Examples:
* Underage drinking. If it's legal for someone to drink, I think it's in general ethical. If it's illegal, I think it's in general unethical.
* Tax avoidance strategies. If the IRS says a strategy is allowed, I think it's ethical. If the IRS says a strategy is not allowed, I think it's unethical.
* Right on red. If the government says right on red is allowed, I think it's ethical. If the government (e.g. NYC) says right on red is not allowed, I think it's unethical.
The VW case was emissions regulations. I think they have an ethical obligation to obey emissions regulations. In the absence of regulations, it's not an obvious ethical problem to prioritize fuel efficiency instead of emissions (that's I believe what VW was doing).