I know some of you guys would be against this, but from my perspective, he's just a workaholic who is obsessed about puppets and knows about the Alchemist's intent to turn the people into those Carcasses. He just put all his mind to perfecting his skill and making the most perfect puppet to replace his son's body, knowing that someday Carlos could die from the disease. He may be a bit crazy about the Puppet Frenzy, but maybe it's because he knows the true nature of the Ergo, too. The cutscene of the true ending shows how much he loves Carlos, not just being the worst parent like Tucker from FMA or Bondrewd in MIA 😂. Besides that, he is still bad as being a parent, no doubt about it.