The term "meritocracy" has been thrown around a bit lately in discussions of income inequality and social mobility. It's worth asking what an alleged meritocracy would look like, and what social mobility might exist there. Here are a couple of cases:
World A -- Human Capitalocracy: The smartest, hardest-working, best-prepared, and most diligent 25-year-olds grow up to occupy the dominant financial positions by the time they're 55, without benefitting from family advantage in a forward-looking sense, though of course how smart, hard-working, well-prepared, and diligent you are at age 25 will in part be a product of your schooling, your childhood peer group, your parents' efforts, etc.
World B -- Genetic Aristocracy: The newborn babies with the genes most inclining them toward hard work, greed, and market-rewarded abilities grow up to occupy the dominant financial positions by the time they're 55 without benefitting from family advantage in any way. In the genetic aristocracy either ex ante differences in family circumstances are so small as to not matter, or social service provision is so generous and effective as to cancel them out.
The important thing to note about this, is that I don't think any of the people who currently believe in more generous provision of social services and more redistribution of wealth would stop believing in either of those things if they became convinced that we now live in a Human Capitalocracy or a Genetic Aristrocracy. Now what is true is that the focus of the egalitarian political agenda would change according to whether you thought we were living in World A or World B. In World A, where accidental swapping of babies in the neonatal ward leads to drastic changes in life outcomes, there's a strong case for large increases in various kinds of social policy interventions. In World B, where accidental baby-swapping is irrelevant, there's a strong case for just giving poor people more money because it's the right thing to do.
I don't think American society resembles a pure version of either of those things, but the more important point to keep in mind is that a meritocracy is not necessarily a very admirable place, unless it's also a humane society in which people are enjoying a high quality of life.