Because it's self evident. Historically extreme inequality generally led to social and economic instability (e.g. the collapse of the Roman republic, French/Russian revolutions/what is happening now) and to misallocation of resources and other suboptimal outcomes.
Obviously aiming for absolute equality would probably be more harmful. But there are plenty of arguments on why excessively high inequality is bad for the society as a whole. If you never bothered to read them and resort to silly conjectures like: "well, it's wrong because people kept saying so since I was young, duh!". Well...
It's not self-evident, as there are plenty of counter-arguments, including the Chinese Empire, the Egyptian Empire, the British Empire, the Caste System in India (going strong for over 3 millennia), and so on. Most of human history has been a period of extreme inequality. All you've got is a handful of revolutions in the last 500 years?
You actually need to make a moral argument. For example, slavery is bad not because it caused the the Civil War, but because it's morally wrong (and there's plenty of arguments here). I've also yet to see a very crystalized train of thought as to why inequality (maybe even extreme inequality) is morally wrong.
Assume civilization has the perfect capacity and amount of resources to meet the basic needs (however that's defined) of all people.
Inequality here might be worse than a different civilization where we are in extreme abundance.
If one person has 99% of wealth and everyone else shares 1% - but that is still enough for everyone to have a good life - then it probably matters much less than the same amount of inequality when there's just enough resources.
So I think the amount of resources and the level of inequality matter - not just inequality in general.
Additionally, it matters what the people with most of the wealth are doing. If they're spending it mostly on orgies - that's probably not great. If they're spending it on making advances that we wouldn't otherwise invest in if things were equal - then I'd argue that's good.
All of this is going to be highly subjective based on what you think is basic needs and a good life and how much envy you have.
> So I think the amount of resources and the level of inequality matter - not just inequality in general.
Yep, I think I agree with this, although I've often seen stuff like "Elon Musk/Jeff Bezos/Mark Zuckerberg shouldn't have that much money. No one should."
So I think the typical anti-inequality argument has a much stronger conclusion.
Isn't moral argumentation subjective though and based on the moral premises an audience is willing to accept? How can one make a crystalized train of thought that withstands the subjective nature of all audiences, when the spectrum of humanity ranges from billionaires and cannibals to popes and middle school teachers?
Or perhaps I'm incorrectly inferring from your use of the word "crystalized" that you're looking for near undefeatable resiliency.
> including the Chinese Empire, the Egyptian Empire, the British Empire, the Caste System in India
Yes. All of those were indeed miserable places to be if you were poor or did not have right skin color etc. I agree.
> You actually need to make a moral argument. For example, slavery is bad not because it caused the the Civil War, but because it's morally wrong (and there's plenty of arguments here)
No necessarily. I'd prefer to make an utilitarian argument. Over long periods of time high inequality leads to inefficiency due to wealth accumulation across different generations.
I could try and make more arguments, but I'll let you have a go this time..
Obviously aiming for absolute equality would probably be more harmful. But there are plenty of arguments on why excessively high inequality is bad for the society as a whole. If you never bothered to read them and resort to silly conjectures like: "well, it's wrong because people kept saying so since I was young, duh!". Well...