If the co-op is sold at a profit, and those profits are distributed to the workers (who obviously all put in the exact same amount of work and time, right?) then they are profiting off the work of others, aren't they?
Second, yes the profit in the marketplace is still exploitative to a degree, but we don't have a viable alternative so there's not much to do about that. I don't believe there's much point critiquing something when there's no alternative.