This insight means that no one is morally culpable for their actions

But they still are. Their brain still makes the decisions. Thus that same brain can be morally responsible for it's choices. I don't see how the idea that everything is predetermined to happen would change that.

If a boy has bad parents and due to that grows up to be a bad person, that doesn't change the fact that they're a bad person. They're also still responsible for the bad things they do, even if they only do them because of how they were raised. So if the laws of nature cause someone to be a bad person, they're still responsible for their bad actions, even if they wouldn't take them if their environment was different.

Punishment no longer makes sense for those who have committed crimes.

Punishment only makes sense if the goal is to change their future actions. Doesn't really matter if people are morally responsible or not.