Robinhood Gets Almost Half Its Revenue in Bargain with High-Speed Traders

Can someone more knowledgeable than me tell me if this is a bad thing? AFAIK, pretty much every broker (except notably Interactive Brokers) sells trades to these types of places to actually perform the trade.

I'm more surprised that it's only half. I didn't think their Gold platform or whatever they call it would have though uptake to really impact their bottom line (their target market is cheap millennials who prefer free to good, and $6/month is quite a bit).

Are they doing anything less ethical than their paid competitors?