My position is basically that enormous market power is like a ticking time bomb. It's not going to work to try to patch over it with specific prohibitions like the one you mention, because big companies will always find loopholes, use their market power to exploit them, and use their wealth and "too big to fail" status to drag out any attempt to enforce the rules. It is an endless game of whack-a-mole that can never work. It's better to just limit the total power of companies to do anything; doing so will also limit their ability to do harm of any kind.