I agree with most of the points in this article, but yet it underestimates a fundamental difference between two ways of disagreeing.
Take the typical political debate about "raising taxes on the wealthy to give social help to the poor" vs "giving tax cuts and reducing social help". People can disagree on that topic for two completely different set of reasons.
People can disagree on that topic because, even if they share a more-or-less common utility function, in which having people dying of cold in the street is valued very negatively, they have different expectations about what each policy will do. Some will say that raising taxes on the wealthy and giving the money to the poor will improve the living conditions of the poor, without hurting much the wealthy, and will be good for the economy since it'll increase the demand in construction/good factory/... which is the true motor of economy. Some will say that raising the taxes on the wealthy and giving the money to the poor will lower the incentive for the rich to invest in the economy, and for the poor to find themselves a job, and will at the end damage the whole economy and makes everyone poorer on the long run. I've my own opinion on that (and I may very well be reflected by the way I formulated the two hypothesis, but that's really not my goal here, so please accept my apologizes if it's too obvious). That disagreement is not easy to settle (or it would have been settled since long), but can be argued rationally, looking at history, at different countries, making prediction on what will happen when a country changes it's welfare/tax policy and checking the prediction later on, ... Labeling "evil" someone who share a similar utility function but disagree on the ways to maximize it is indeed a catastrophic mistake.
But people can also disagree on that topic because they have different utility functions. Some do think that homeless are people who deserve to be homeless because they were too lazy and stupid, and give a positive value to the fact that lazy/stupid people are punished. Some others do not include any significant term in their utility function for the homeless, considering they are only a tiny part of the population and not worth considering. Some others do think that having rich people is in itself unfair, and that taxing them highly, even if it doesn't reduce poverty, increases fairness and is therefore valued positively. Disagreements between people having different utility functions like that will be much, much harder to settle. And labeling "evil" someone who has a broadly different utility function than yourself is much more understandable. If we don't for that, well, for what is the word "evil" ?
And it gets even more complicated, because you can have people who claim they share your utility function, while in fact they don't. And you don't always even know for sure if they are or not. And because it's often a bit of both - people who favor high taxes/social help and those who favor tax cuts/no social help usually have both different pondering in their utility function and different expected outcomes for the two policies.
You pose a number of excellent questions in your comment that one might ask about a political opponent. So then the next step is: how does one go about answering those questions? How do you figure out whether one's opponent has different terminal values, or different instrumental values, or both?
We see far too direct a correspondence between others’ actions and their inherent dispositions. We see unusual dispositions that exactly match the unusual behavior, rather than asking after real situations or imagined situations that could explain the behavior. We hypothesize mutants.
When someone actually offends us—commits an action of which we (rightly or wrongly) disapprove—then, I observe, the correspondence bias redoubles. There seems to be a very strong tendency to blame evil deeds on the Enemy’s mutant, evil disposition. Not as a moral point, but as a strict question of prior probability, we should ask what the Enemy might believe about their situation that would reduce the seeming bizarrity of their behavior. This would allow us to hypothesize a less exceptional disposition, and thereby shoulder a lesser burden of improbability.
On September 11th, 2001, nineteen Muslim males hijacked four jet airliners in a deliberately suicidal effort to hurt the United States of America. Now why do you suppose they might have done that? Because they saw the USA as a beacon of freedom to the world, but were born with a mutant disposition that made them hate freedom?
Realistically, most people don’t construct their life stories with themselves as the villains. Everyone is the hero of their own story. The Enemy’s story, as seen by the Enemy, is not going to make the Enemy look bad. If you try to construe motivations that would make the Enemy look bad, you’ll end up flat wrong about what actually goes on in the Enemy’s mind.
But politics is the mind-killer. Debate is war; arguments are soldiers. If the Enemy did have an evil disposition, that would be an argument in favor of your side. And any argument that favors your side must be supported, no matter how silly—otherwise you’re letting up the pressure somewhere on the battlefront. Everyone strives to outshine their neighbor in patriotic denunciation, and no one dares to contradict. Soon the Enemy has horns, bat wings, flaming breath, and fangs that drip corrosive venom. If you deny any aspect of this on merely factual grounds, you are arguing the Enemy’s side; you are a traitor. Very few people will understand that you aren’t defending the Enemy, just defending the truth.
If it took a mutant to do monstrous things, the history of the human species would look very different. Mutants would be rare.
Or maybe the fear is that understanding will lead to forgiveness. It’s easier to shoot down evil mutants. It is a more inspiring battle cry to scream, “Die, vicious scum!” instead of “Die, people who could have been just like me but grew up in a different environment!” You might feel guilty killing people who weren’t pure darkness.
This looks to me like the deep-seated yearning for a one-sided policy debate in which the best policy has no drawbacks. If an army is crossing the border or a lunatic is coming at you with a knife, the policy alternatives are (a) defend yourself or (b) lie down and die. If you defend yourself, you may have to kill. If you kill someone who could, in another world, have been your friend, that is a tragedy. And it is a tragedy. The other option, lying down and dying, is also a tragedy. Why must there be a non-tragic option? Who says that the best policy available must have no downside? If someone has to die, it may as well be the initiator of force, to discourage future violence and thereby minimize the total sum of death.
If the Enemy has an average disposition, and is acting from beliefs about their situation that would make violence a typically human response, then that doesn’t mean their beliefs are factually accurate. It doesn’t mean they’re justified. It means you’ll have to shoot down someone who is the hero of their own story, and in their novel the protagonist will die on page 80. That is a tragedy, but it is better than the alternative tragedy. It is the choice that every police officer makes, every day, to keep our neat little worlds from dissolving into chaos.
When you accurately estimate the Enemy’s psychology—when you know what is really in the Enemy’s mind—that knowledge won’t feel like landing a delicious punch on the opposing side. It won’t give you a warm feeling of righteous indignation. It won’t make you feel good about yourself. If your estimate makes you feel unbearably sad, you may be seeing the world as it really is. More rarely, an accurate estimate may send shivers of serious horror down your spine, as when dealing with true psychopaths, or neurologically intact people with beliefs that have utterly destroyed their sanity (Scientologists or Jesus Campers).
So let’s come right out and say it—the 9/11 hijackers weren’t evil mutants. They did not hate freedom. They, too, were the heroes of their own stories, and they died for what they believed was right—truth, justice, and the Islamic way. If the hijackers saw themselves that way, it doesn’t mean their beliefs were true. If the hijackers saw themselves that way, it doesn’t mean that we have to agree that what they did was justified. If the hijackers saw themselves that way, it doesn’t mean that the passengers of United Flight 93 should have stood aside and let it happen. It does mean that in another world, if they had been raised in a different environment, those hijackers might have been police officers. And that is indeed a tragedy. Welcome to Earth.