IMO the main problem is the existence of an institution that is (arguably) more powerful than any government in the world.
That's not necessarily a problem on its own.
It becomes a problem when those same institutions have a very small number of people with specially concocted classes of shares that give people like Zuckerberg majority control of the company despite owning < 30% of actual shares.
I don't want to live in a world where 1 person can have such immense and unchecked power. Especially when that 1 person is immune from, for example, being removed as CEO.
I'm not sure if it's still the case today, but I believe Sergy / Larry had 51%+ control of the company despite only owning ~10% of shares.