alt Hacker NewsCapitalism is not simply free markers - it means "control by people with capital." People control society proportionally to how much capital they have, and those who control vast boards of capital are very uninterested in allowing capital to be spread around more equitably.
The parent post is not even the worst offender. In his (otherwise good) https://en.wikipedia.org/wiki/23_Things_They_Don%27t_Tell_Yo..., Ha-Joon Chang completely flips the meaning between free markets and capitalism.
I would say that capitalism is not only characterized by private ownership of capital, but also by free market for labor, which could be almost considered a complementary feature (other side of the same coin).
On the other hand, socialism primarily rejects free market for labour in favor of worker emancipation and participation in decision-making. So both socialism and capitalism are compatible with free markets; it's the labor market where the opinion differs.
(As a socialist, I would add, salaries cannot be treated in economics the same way as e.g. price of apples, because apple doesn't care what its price is.)