I'll rephrase the question. How do we know it's a normal family? How can we be comfortable?
The types of abnormalities that would impact on parenting time are starkly obvious. A very broad range of parenting produces healthy children. Your average person, if they love their children, if they try hard, if they're there for their children, do a little reading, they're normal. Any abnormalities will stick out like a sore thumb. It is that group of people—the vast majority of our population—that we say the exercise, the cost, the conflict, the stress on the children, is not worth the upside, because the end result might be that you don't get 50% but you get 37.2%. However, if you're not normal, you'll still damage the children.