Earlier quoted context omitted.
As far as I understand it robinhood makes (most of their?) money from selling their order flow to hedge funds.
Which is not remotely illegal, and most brokers do the same thing, except they used to charge people to buy and sell as well but now just make money from order flow. In fact market makers have always been involved in stock sales to ensure a fluid market; none of this is new. What is new is that buying and selling stocks costs you nothing, so there is no barrier to anyone to put money in or take it out. While everyone…
Similar to Google or Facebook, if I get the service for free, the service-providers' incentives may be aligned against me in favour of their paying customers.