First of all, the existence of a social norm is different from a law, and we were discussing the former, not the latter. It's true that if you have reason for a social norm, you might have reason for a law. But it may be that the norm would be overall beneficial, and the law overall harmful.

If having a norm or a law against something means that people are not agents, then people are not agents because there is a law against murder. So obviously that does not follow. If you want to call that "taking away agency," you can, but people are still agents.

Are you saying that society would be better off overall without any norms or laws? And would you push a button to bring about that state of affairs?

To push the button in your scenario I would have to be very certain that it would be beneficial overall, including the fact that I was pushing a button like that. I am not that certain, so I would not push it.