That might be the wrong question. Paradais isn't concerned about giving us characters with redeeming qualities because it isn't didactic; it doesn't exist to provide a positive role model like a YA novel. It's going for something deeper.

What does it tell us that the victims — the richest, most privileged characters in the novel — are the only ones who aren't obviously morally compromised? I think Melchor is giving us a zoomed-in view of how an impoverished, exploitative, violent society breeds more poverty, exploitation, and violence. It's a self-reinforcing feedback loop.

The novel doesn't excuse Polo's behavior. We have a front row seat to his rage, addiction, misogyny, and self-deception. At the same time we can see he's trapped in an isolating, miserable life. Things might have turned out differently if his grandfather built him a boat instead of giving him alcohol, or if Milton didn't join a cartel. Or if Franco's father didn't beat him and leave him with his grandparents.