> Although the harm suffered on each trade is minuscule — fractions of a cent per share — the aggregate kickbacks amount to billions of dollars a year. That's

> Although the harm suffered on each trade is minuscule — fractions of a cent per share — the aggregate kickbacks amount to billions of dollars a year. That's the money quote. 99% of retail investors should be buying stock infrequently, maybe once a month when the paycheck comes in. Ideally you're buying one or a few index funds, so the total number of transactions is small. If you're in that boat, this order-of-fulfillment tax really doesn't affect you and can be entirely ignored. Your returns are really only in danger of being dragged down by this thing if you're executing many trades per day. But if you're doing that, you had better be a sophisticated investor anyway, or else you're definitely losing money.