Straw man alert.

Nobody is suggesting people should all be "equal".
Nor is the very large degree of inequality of wealth in US society something that is an automatic consequence of "reality". It is the outcome of choices as to how society is organised. Western European free-market societies are nothing like as unequal as the USA.
The obvious drawback to the choice to tolerate extreme inequality (and it is a choice), as seen for instance in parts of S America, is that it leads to a weakening of social cohesion. The "have nots" feel the institutions of society do nothing for them and perpetuate what they see as injustice. They cease to feel respect for the law, in particular the property rights of the "haves", leading to an increase in crime and a breakdown in order. This process led to the French Revolution, for example.
What makes matters especially bad in the USA is that there is no restriction on donations to fund politicians or to limit the use of money in political campaigning. So there are in fact quite good reasons for the "have nots" to suspect that the "haves" have sewn up the political system to lock in a permanent advantage for themselves.
Arguing that the current state of affairs is just inevitable won't do.