I’m not following this disagreement enough to know if I agree with anyone in general, but I do think this single sentence is eminently correct.
There is a weird human bias to talk about justice for all, except the guilty. But surely justice is as much about the guilty as the innocent? Justice is what determines guilt. But we talk about other people like they need to earn their humanity, rather than have it be intrinsic to their existence.
I think a big barrier is that when people do awful things that reject the humanity of others (like murder, rape, genocide, etc.), we feel entitled to also reject THEIR humanity - that feels like justice to us, in an “eye-for-an-eye” sense. We’re all getting along fine, and then you go and murder someone, and now we get to murder you. That seems fair, just, and right.
For a hyperbolic example, if someone comes to your house to kill your children and you have a gun, you shoot first, and ask questions about their motives and life choices later (or never). I’d expect most people to react the same way. In order to react that way, psychologically, you HAVE TO make that child-murderer a non-human, a valid target, and murdering children is a damn fine way to become a valid target.
But imagining a child-murderer as a complex human being worthy of respect and life means that you recognize that this reprehensible action isn’t from a place of inexplicable, otherworldly monstrosity. Because you are both human, there’s a possible world in which you could’ve been a child-murderer yourself. In asking and answering questions like “How could I ever become someone who goes around murdering children?” you can help stop the next potential child-murderer before they can even act (because you work toward a world where mental health isn’t stigmatized, for instance, and reasonable gun-control is in place based on mental health evaluations that are as regular as doctor’s check-ups). You can’t ask that question if you see that child-murderer as simply an inhuman monster.
Dehumanizing and shooting the child-murderer in the moment isn’t wrong - it’s necessary, even. But it needs to be seen as unjust, despite that - a tragic situation that we can prevent by changing our society, not a one-off hero vs. monster scenario.
That moral ambiguity - that you can shoot someone who is killing your children and still not be totally right, that you can do something necessary and that felt good and that anybody should do ant it still not being the most moral thing to do, that you have a responsibility to the person who is killing your children - that’s tough for humans in general to accept. It’s downright impossible for a Fundamentalist world-view to even acknowledge as a thing that happens - when the world is morally black and white, the child-murderer is evil and the man who shoots the child-murderer is good, period.
Which leads the Fundamentalist society to have more child-murderers, despite all the good people who fight against evil that they have. Because they don’t understand how child-murderers are made, they never address the root of the problem. Every one is just a one-off monster, and anyone who MIGHT be a child-murderer is probably a monster in the making, basically inhuman.
Which is why, despite all the mass-shootings that have happened in the last 12 months or so in the US (including an actual massacre of children), we’re not really any closer to addressing the root of the problem. We’re all worked up fighting black/white moral battles against “crazy gun nuts” or “liberals who want to take away my rights.” We’re used to fighting those battles - they’re easy for us to fight. Clear black and white. Very Fundie-friendly.
We’re less comfortable saying “Mental health is important for everyone,” than we saying “Gun owners have blood on their hands!” or “Bad people should be shot!”
Heck, Michael Moore falls prey to this problem quite a bit himself - he’s a product of Fundie Culture as much as Rick Santorum is. Which is why he’s usually at his best when he’s humanizing others - showing that “bad people” aren’t so bad, looking for the good in the world and holding it up for consideration.