> All happy families are alike; each unhappy family is unhappy in its own way.
One thing I think isn't being emphasized is that those authors aren't saying "parenting doesn't matter" as much as they're saying "you have little control over what kind of parental environment you provide, so relax and do the best you can".
You don't control your genes, your kids genes, and you don't control your environment. Those are the (super overly simplistic) factors that comprise parenting.
Another way to look at it is that, given your genes and the way you were raised, you're going to be a certain kind of parent. Given your kids genes, the way you raise them, and their experiences, they're going to be a certain kind of adult. You don't have control over any of that as a parent, so relax and enjoy the ride.