The problem is how do we get there? In a market there will always be actors powerful enough to corrupt the governmenta and influence regulation in an undemocratic way.
Even in a market dominated by socialist companies where workers have power. Workers having ownership isn't some panacea against corruption and willingness to dominate others. You can still end up with a company full of terrible people who have no qualms cornering a market and then committing to rent-extraction. They can even commit to those horrible practices in an internally democratic way!
If the working population is deciding the laws democratically, then there's a good chance of laws against monopolies and trusts being more binding than they are under capitalists, not that I care as much about the co-op model of socialism.
It's impossible, as has been demonstrated throughout the last few centuries of history. Even in cases where a government makes a massive shift towards a pro-worker position (i.e. the New Deal), over time the country will fall back into regulatory capture and devolve to an oligarchy.