It’s probably more accurate to state that they believe capitalism and markets to be two separate things, for example a market economy where every business is a multi-stakeholder worker-consumer coop and workers and “consumers” alike can consent to what happens at work, would be at odds with private ownership given that everyone is an owner with decision making power (collective/socialized ownership). This is pretty much what Corbyn and the Labour party a few years back were aiming for - they were going to experiment with cooperatives by having the government encourage and fund them.