Because we have the knowledge and technology to live comfortably with a lot less manpower then 300 years ago

That's human nature, not capitalism. People get used to comforts. People don't like sharing what they see as theirs. This has nothing to do with private ownership of industrial equipment, and operating it for profit.

Sure, you can come up with a political / economic system where everything is divided up evenly. But, that goes against everything we know about human nature. People are selfish. They might be willing to share with their immediate family, or maybe even their clan / neighbourhood. But, people don't tend to sacrifice their comforts so that people on another continent who speak a different language can have a better life.

Look at pre-capitalist societies, were they full of egalitarianism and justice? You can't blame capitalism for human nature.

It's not caused by capitalism but exacerbated by it. The ratio of workers to retirees in 1960 was 5.1 to 1, it's now 2.1 to 1. Sure if capital wasn't extracting excess value maybe we could be fine at 2.1 to 1 but I doubt we would be at .5 to 1. At some point it becomes an issue