You can’t blame the parents
What kind of parents were Adam and Eve if their first son becomes a killer? Could they really be expected to have done any better? Cast out by a thoughtless, heartless, vengeful, evil God for being too innocent to see through the deceptions of a being almost as powerful as God himself, left to fend for themselves with little or no guidance from their creator (we didn’t ask to be created, you know!), it’s no surprise they did such a piss poor job.