If a person is waving a gun there is nothing stopping people from trying to stop him

I think you two agree on that, he is saying that you should stop a person like that, and you're saying the same thing. The problem is that he believes that laws do anything besides blanket us in a false sense of security which endangers us much more than protects us, or than it could protect us.

That's why it's ok to stop someone from endangering others.