The biggest political divide is actually optimist/pessimist not left/right I think the general idea on the Nietzschean parent is something like: “life is valuable and I desire a parent-child relationship; though their lives may be filled with hardship and struggle, I will guide my child and help them any way I can. They are likely to enjoy their lives, but I will aid them in a journey to establish meaningful and productive lives through their hardship.”
Because Schopenhauer1 supports a non aggression idea for ethics, it’s pretty clear why this wouldn’t be okay. Nobody needed to come into existence, but some would-be parents have a strong interest in procreating and I don’t think it’s clear that just because something didn’t have to be it’s always impermissible. I don’t think this idea renders procreation 100% impermissible for those who don’t support a non-aggression pact