It's a dark pattern, but there's nothing illegal about it. Their privacy policy states "We may also share information with others in an aggregated or otherwise anonymized form that does not reasonably identify you directly as an individual." Knowing that there exists someone who is about to buy TSLA does not identify that person, and yet is still incredibly useful to a market-maker. Selling data you've collected (without identities attached) is legal and largely unregulated. And the actual transaction is an ordinary B2B customer relationship.
Amazingly, a significant number of Robinhood customers are aware that they do this and don't care.
Amazingly, a significant number of Robinhood customers are aware that they do this and don't care.