Imagine where Capitalism would be if say... everyone started with a $1 but you can only make $2 profit max? No, there was always someone who wanted to make $10 profit. Followed by $1000. And then a million, and a billion and now a trillion.

Now, you could stop this process, but that's exactly how you end up with Socialism.

Fine, everyone now makes $100. But everything is also worth $100 max. And because there's no longer an incentive to increase profits, society as a whole stagnates or worse. Mass starvation.

The USSR vs USA was already a textbook example of why this can't work. The Soviets tried to catch up with America by putting out higher and higher production quotas while also having to fulfill their own consumer needs, but it just crashed in the end.