> There's nothing inherently wrong with inequality
If you're talking about a spherical economy in a vacuum, no, there isn't.
When we actually turn our attention to the real world, we find that, in fact, there is. Because when the people at the top have sufficiently disproportionate power (and wealth is a kind of power), they use that power to increase the inequality by any means necessary. That includes, fairly prominently, redirecting resources that would otherwise have gone to ensuring the floor stays high to raising their own ceilings.
So it's not a binary—either there is perfect equality or everything goes to shit—but the levels of inequality we have today are demonstrably bad for society.