This sort of econ101 argument that MR=MC in a fully competitive market forgets that such a simple model also must allow for consumer surplus to equal supplier s

This sort of econ101 argument that MR=MC in a fully competitive market forgets that such a simple model also must allow for consumer surplus to equal supplier surplus, and that they must necessarily also be zero. In that case, all transactions have zero net benefit for all parties involved, and you might as well not have any transactions.