The honest answer? We've been taught that it's wrong since birth. If you go read some (not really) edgy takes on 'honor' codes from the middle ages, you'll find a theme that the codes really just made it hard for peasants to go after nobility types without breaking the codes. Think about stuff like fighting one-on-one rather than mob rushing, using poison, not stabbing someone in the back... All things that would allow a peasant, or 20 peasants with knives, to kill an armored man. Also all things that were consistently done between noble people, but conveniently ignored unless useful politically.
Meanwhile, most things that we would consider moral are completely left out of such codes. And even back then, many of those morals were around, they just weren't important to said codes of honor.
Nowadays, the same propaganda is used against us. You can't hold a person working for a company responsible for the company's policies/actions... unless they're below a certain pay-grade, then it's all their fault. You can't get angry about your health being impacted by pollution, because how dare you try to change someone else's life that uses that pollution! How dare you feel frustrated because someone can afford multiple giant boats and staff andmultiple estates and their staff... while you struggle to afford rent and food and others languish on the street without any help at all.
All out war and violence .... that's what's stopping us.
If we ever attempted that, we would be easily manipulated into thinking that it was a war for other reasons and generally break down into a general war.
And at the end of the fighting, the rich and powerful would take over the narrative of why the war started.