Yeh yo, just because something is 'normal' doesn't mean that it's right. Owning slaves used to be normal. It's only through questioning the status quo that change happens.
Medical benefits of circumcision are bunk. It's a cultural tradition, that's all. We don't do it because it's good for kids, we do it because 'well, that's just what we do, it's what we've always done'. That sort of reasoning, 'appealing to tradition', is a logical fallacy.