"But people are sometimes authoritarian and cruel! Just for fun! And the only people who you can be consistently cruel to without them slugging you, shunning you, suing you, or calling the police on you are your children. This is a reason for more than the usual amount of skepticism of arguments that say that strict parenting is necessary."

That's a very good point. But there may be a parallel counterpoint: "Sometimes parents are indulgent and too lazy or exhausted or undisciplined to enforce an appropriate degree of discipline in their own children. And the one relationship in the world that is probably most often characterized by unquestioning, adoring love is that from parents to their children. This is a reason for more than the usual amount of skepticism of arguments that say that liberal parenting is necessary." Nothing makes most (... or at least many?) parents happier than making their children happy — so shouldn't we expect a bias toward indulgence too?

Perhaps it would be better to weight our arguments about appropriate parenting styles based on the personalities of particular parents.