In the absence of private actors, the tendency of the state-run actor is to be inefficient. However, efficiency is not the only goal, and it should not be the state's main goal. Otherwise, you won't e.g. have emergency services capacity in reserve for rare but severe events. They get cut for "efficiency ".
In the absence of state actors, the tendency of private actors is to maximise profits and extract rents. But this is not the best thing for the larger society.
Therefor, the presence of each keeps the other honest. Specifically, we must distinguish the presence of state-run grocery stores from the straw man that you construct where there are only state-run grocery stores.
I think this is a misconception.
In the absence of private actors, the tendency of the state-run actor is to be inefficient. However, efficiency is not the only goal, and it should not be the state's main goal. Otherwise, you won't e.g. have emergency services capacity in reserve for rare but severe events. They get cut for "efficiency ".
In the absence of state actors, the tendency of private actors is to maximise profits and extract rents. But this is not the best thing for the larger society.
Therefor, the presence of each keeps the other honest. Specifically, we must distinguish the presence of state-run grocery stores from the straw man that you construct where there are only state-run grocery stores.