This is true, but not overly relevant in this context - the reason lack of commission was mentioned was because someone said that fees will eat away at a day tr

This is true, but not overly relevant in this context - the reason lack of commission was mentioned was because someone said that fees will eat away at a day trader's profits before a down market will affect them; with Robinhood or other commission-free brokers, that will not be the case (regardless of how the broker is profiting off the trades - the trader is still going to be getting the best price available on the market, as required by law)