There are huge swaths of people doing the work required to make it better, every day. It's not as easy as turning a dial from "bad" to "good"
Unless the person above is, of course, an anarchist who has no answer for what to do about Richard Ramirez, Ted Bundy, Jeffrey Dahmer, Phillip Garrido, or Brian Mitchell. I would say that as imperfect and heavily flawed as our system is, "Perfect is the enemy of good."
Nothing. Those people are one-in-a-million anomalies. If it weren't for the media hype surrounding them, their impact on society would be comparable to the impact of deaths from lightning strikes. What do we do about people being struck by lightning? Nothing.