As others in this thread have noted, what you described would be illegal. But suppose for the sake of argument that Robinhood's order flow is actually really bad and users are getting a measurably worse price through RH vs other brokers. RH targets small-time investors who are trading in small amounts - perhaps investing a bit of their paycheck every week. It seems unlikely that the order flow would be so bad that RH users are losing anywhere close to $5 per trade because of it.

So even if "it's not really free" it's still a significant discount compared to the pricing that was standard before RH came along. Opening up investing to more people by making smaller & more frequent trades feasible seems generally good to me.

I will admit that other aspects of Robinhood's business such as the degree of gamification are still concerning, though.