Why do people (waste their time) hating each other?

As the saying goes, "hurt people hurt people". A personal story: When my childhood family moved to a promising white working class neighborhood one of the neighbors saw our large family and yelled "go back to slummy neighborhood you racial slur". But my family did then proceeded to them move 13 people in a 3 bedroom home along with noisy roosters/chickens in the backyard. So admittedly their assumed stereotypes had merit.

30 years later only my parents remained in the house and the neighborhood racial profile changed significantly. My mother said "I don't think I could sell to someone from the new ethic group". When I asked, "Why?!", she said, "because they'll put 10 people in the house". When I reminded her we once did the same she snapped, "That was different!". The way she snapped was a clear indication she still felt pain from what had happened many years ago.

To add further to my opening quote, I have taken severe beatings, as in decades of physical pain followed, based on my ethnicity but I hold no grudge in part because I am financially secure and physically strong now. So I no longer "hurt" in a sense or naively feel like I can be hurt. But my poorer family still talks about my beatings with a grudge against the entire racial group of my attackers.

Some other research that is relevant, sorry I don't have a source to link, but it is shown that a stressed rat will not suffer stress related health disorders if you give it a smaller rat it can periodically beat up. More optimistically it will also avoid negative health consequences if you give it something enjoyable to do (e.g., a stick to gnaw). But hobbies are unfortunately a luxury for many people whereas hate-speech costs nothing.

Finally for most of human history it was prudent to distrust anyone outside your tribe. With the standard brain OS, negative emotions rush in and humans explain their poorly understood emotions with knee-jerk stereotypical views. Also have some perspective: for example if your home was your number one asset would you happy to have my childhood family move next door ? Doubtful. Sometimes anger is an understandable reaction but how to keep it from escalating to violence or being exploited politically is a larger concern.

It's an attachment defense response: if your culture is a favored child, and some other culture is mean to it, you must defend your culture however you can. But - crucially - the other culture doesn't have to be mean or actually do anything. Instead it can be a scapegoat for a failing of the child: "We are good and pure here, therefore they are to blame for our troubles." This manifests in incoherent narratives where the enemy is monstrous yet pathetic, strong yet weak, devious yet dumb. Thus, as you see problems pile up with your favored son, you become increasingly infuriated at the outsiders who are to blame, and seek justice against these obvious evils.

Swap culture for race, creed, wealth, sexuality and so on and you get all the -isms and -phobias in the world. People who are at ease with the status quo can disengage with their phobias, even if they still lurk in the background. We all have a few, and our emotions try very hard not to let us see our bias up close.

As well, the parent-child roles are flexible but recurring, and scale up and down in strange ways: if we beg our government to do more for us, we are the children. If you observe a celebrity being childish on Twitter, the defenders of that celebrity are acting as parents.

For a deeper dive philosophical investigation, see Heather Marsh: The Creation of Me, Them and Us.

People start drama irrespective of circumstance. It is a constant, of sorts, regardless of how good or bad they have it.

At a societal level, good times bring petty drama, bad times bring people together as they can fixate on their shared negative circumstance. Usually there is some scapegoating involved, which is just a shared fixation that satisfies this urge.

I can't say I'm immune but Marcus Aurelius and Seneca have some interesting words on the subject. Best read for yourself if you are interested.

Because we evolved in tribes that competed with each other like our chimp cousins. Read "Moral Tribes: Emotion, Reason, and the Gap Between Us and Them"

I would suggest reading On the Pleasure of Hating by William Hazlitt

Personally... a significant portion of people like to "right". Some base their identity on it. People who are "right" in some things will often believe they are "right" in all things, which they may or may not be "right" in, even if they are sometimes unsure. It is these things that people will argue most vehemently in order to be "totally" right for any humility would be seen as total defeat. Some do it unconsciously, and some, more worryingly, do it consciously.

Someone has to be at fault for why you are held back. That’s the root of much of it.

Think of how many more at HN think they would have gotten into Stanford, Harvard, MIT, etc if it weren’t for affirmative action.

Conflicts based on land and resources - and cultural and political supremacy (often in the service of resource control and the police power to enforce it) - are hard to resolve equitably and peacefully, and tend to produce winners and losers who are naturally antagonistic toward each other.

Land in particular seems to be a largely zero-sum game, so a win-win outcome seems unlikely.

If the winners and losers divide according to culture, heritage, religion, social class, etc. then some identity politics and attitudes may mirror or reinforce the conflict.