What I'm after is that much of the ethics by which our legal system operates, e.g. a BAC limit for legal driving, is divorced from moral questions such as: "Is drinking beer a sinful act?"
I think you’re gravely misguided. BAC has nothing to do with sin, it’s connected to the morality and ethics of putting your fellow citizens at risk of your impaired driving.
My repeated point has been that morality != religious sin, rather the latter is a subset. I don’t necessarily agree with laws/taxes in this regard, but it’s important to understand where they come from.