Selling order flow isn't "selling the poor out". Reg NMS literally requires brokerages to route your orders to where they will get the best execution price. In general you as a retail investor get better execution prices because of how this works (why? because retail investors generally don't have new information that will move the price so they are "safe" trades for liquidity providers).
Now robin hood _did_ get fined for "not perform[ing] systematic best execution reviews of several order types". If that's what you were referring to then fine. But if your complaint is just about selling order flow you should better understand what that means. Maybe start with patio11's How Brokerages Make Money[0].
