I'm gonna agree with Dinosauriawe on this one.
In the 30s, parents beating their kids was considered normal. And there wasn't anyplace to go until you were old enough to whip your old man's ass and set out on your own. I s'pose there was the possibility of lying about your age and joining the army at 16. But that's just going from the broiler to the blast furnace, isn't it?
Buk did, I think, what he could do. He endured. ("Endurance is more important than truth," he said.) And I believe this crazy and abusive environment in a strange way helped him to toughen up for what lay ahead.
I recently watched a documentary about the building of the Burmese railroad during WW2. The Japanese used slave labor, much of it composed of U.S. and Australian POWs. And the interviewer asked this one guy how he made it thru all the torture, malnutrition, disease, and abuse. And he said, "hatred of the Japanese." I think Buk's contempt for his old man may have gotten him thru. It certainly framed his view of mankind.
"Humanity / you never had it / from the begining."