As somebody who does deal with the market the idea that this takes away power from the individual investor is ludicrous! Interactive Brokers offers discount rates where a trade can be carried out costing only 1 USD (American Exchanges) since over a decade. If you think a trade costing you 1 dollar is too much, then maybe you should not be in the market. The fact that others cost say 5 or 10 dollars per trade only shows how lazy the retail investor is because they don't actually research the various brokers.
Now getting to the point of payment for order flow. Imagine you are at an blind bid auction for baseball cards. So you write down that bid that will be given to seller. Imagine for a moment the buyer offers 10, the seller offers 20. You are stuck at figuring how gives and how much. On an exchange that is a guessing game since the buyer and seller don't know each other. But now steps in a middle entity that says, "I will sell you order flow, but to do that I need to know the orders and your clients." Imagine for a moment that the sold order flow shows that the seller is always easy to trigger, and the buyer likes to chase. The order flow could then jack up the price to the buyer for 16 and the seller down to 14, meaning 2 dollars of free money. Is that fair? For that is exactly what happens now with Robinhood. They analyze your behaviour on buying and selling and see how you play the game. Then like Facebook they slice and dice you to make as much money as they can out of you. Of course your trades are "free"...
When this behaviour was done wrt to Facebook people made the excuse, "but facebook does not charge me anything." Well Robinhood does not either, but they cost you profits! Real profits! But [snarkily said] the youngsters would rather gamble their money away...