I think....(and I'm not normally like this)....that it's Satan's work.
CS Lewis does such a great job in Screwtape Letters trying to "get in" at Satan's mind. I think many of the points Lewis makes about different areas of Christianity could be applied to Christian parenting...
....make parents think they have control, in order to turn them away from God....
....use parents to demonstrate violence and hate, in order to turn kids away from God....
....use parents to turn others away from God, by "parenting" in God's name....
....use the fear of the world to keep their kids insulated, so that the spread of Christianity can be slowed/stopped.....
I honestly think that the majority of punitive Christian parents are deceived.