I have a hard time believing a Harvard PhD and rapid support of capitalism has never encountered a critique of the topic outside of a third grader's worldview.
Generally, i don't like the view that there is nothing between radical capitalism on the one side and stalinist communism on the other. And that everything that is not 100% "true capitalism" is automatically socialism hich is, by the above logic, stalinism style communism. Every European country prooves otherwise.
In at least one of his essays he argues that founding a company creates wealth and wealth creation does two things.
1) Makes society as a whole better off. i.e. "A rising tide lifts all boats", so the poorest in society benefit as well as the richest. The mean value of all individual's wealth increases.
2) Increases inequality because the distance between richest and poorest increases. The variance in individual's wealth across the population increases.
Of course, these are just arguments he puts forth. Others may disagree with them. ...but I think it's worth trying to understand the distinction he makes between "inequality", "wealth creation" and "improving society as a whole".
He even once wrote, no idea in which essays, that he would prefer to be poor in an advanced society to be rich in an non-advanced one (something along these lines). Now, as we know that automation and software are enabling companies, and their investors / founders (with VCs investors more than founders IMHO), to create a lot of whealth that is not very well distributed across society. Which we see every day. So, working from his earlier statement on which society he would rather life in had he the choice, I assume PG has some level of understanding about the social realities. He is now also in a position to actually do something about it, him being arguably very rich and influential in his own way.
And what is he doing? Arguing against taxes for the rich to make life easier for the poor, against reducing the economic and social distribution and faisness in society. Because, according to him as far as I understood his later essays, as long as everybody can be enabled to found a company that problem will go away. Which it will not, not everyone can start one, regardless of access to capital. And even then most of the return will end up in the hands of the rich investor class with founders being more often than not cogs in the system.
Call the opposite approch socialism if you want, but if we as a socuiety don't think about these issues, hard, we will end up in deep trouble. Not just in the US where these problems are way more extreme than in Europe. I'm just way beyond believing that rich people will voluntarily do something about the poor if it would cost them a single dime.