I don't think anyone is saying ignore it, just that how you address it really matters. I grew up with a sibling and we got up to all sorts of trouble/fights and our parents were severe about it. all the punishment did was make sure we didn't do x or y in-front of the parents. Like it did teach me to be a great liar and sneak and we got up to all the hijinks, but I don't think that is the ideal parental outcome despite how well it has served me in life.