Capitalism generally allows for a range of ownership structures, including traditional privately owned businesses, publicly traded corporations, and worker-owned enterprises.

I guess an argument would be that privately owned companies are already too wealthy to allow for fair market competition, but in worker owned companies nothing is stopping them from becoming large corporations that can also do everything a private lobbyist company does. If you don't believe me, just look at your democratically elected capitalist government. Just because something is democratic doesn't mean it will be ethical or fair internally or externally.