I saw some research when I was in college that before Deng's reforms in Communist China, the level of income inequality was pretty low. Once the market reforms were enacted, inequality went through the roof.

Markets disproportionately reward those who produce things other people want. That is inherent inequality. The ethical question is how much of that reward could be distributed to others who may actually have a bad lot in life (though my own bias is to doubt the extent to which, barring obvious physical or mental disability, a person is incapable of making her own luck).