What fiduciary duty? They disclose right up front that they are paid for order flow, and I assumed, correctly, that this meant they were allowing Citadel, et al. to front-run the retail orders and skim risk-free cream from the rubes. As a former trader, if you're fine making a donation to Ken Griffin with every trade, I suppose there's little more to say there, but Robinhood markets their service to unsophisticated investors that may not realize that is what they are effectively doing.