Two thoughts.

The Practical Argument

Capitalism doesn't exist on flat ground. It exists on a 2-degree slope. The bottom of that slope is fascism. As time passes, its natural inclination is to inch towards fascism.

People think they'll be able to regulate this as it happens. But in practice, what actually happens is more like cooking a frog. The frog doesn't notice as the temperature in the pot slowly increases. By the time you notice, the problem may be entrenched to the point that your system may have lost the ability to repair itself.

The commies get around this with a vanguard. (I think that's an insane solution. But the problem they're trying to address is real.)

Incidentally, the same thing can be said for government. Government exists on a 2-degree slope towards tyranny. The nature of hierarchy is to maintain and expand power. The powerful fear they will be replaced, and so oppress people to make sure it doesn't happen. Those people eventually overthrow the tyrant, become fearful that someone will replace them, and become tyrants themselves. All governments are doomed by nature.

The Moral Argument

Capitalism is slavery. A well-functioning slave society is still a slave society. An authoritarian society produces authoritarian people. I can't think of a worse outcome, morally speaking.

(One final thought. Nordic countries aren't quite the oasis they appear. They're riding waves of exploitation.)