Second, the real estate thing is a weird tangent. I just don't buy that adding an intermediary to real estate transactions is the win-win-win claimed. This seems like a weird detour to justify Opendoor (which, it should be noted, A16Z was an investor in).
Let me use this as an analogy though. Imagine the NBBO-equivalent for house sales was a 10% broker fee split between buyer's broker and seller's broker. What this post is arguing is that the sale of order flow is fine because most people pay less than 10% this way.
Thing is, once you decide to buy or sell that house, you're doing so without necessarily knowing what the price will be or how much commission you'll pay other than "probably less than 10%". Whoever is processing that is free to take that buy or sell order and then act before processing it. In financial markets, this is called frontrunning. Some markets allow it, some don't.
Worse, you as an investor have less visibility into what's going on because these trades through a variety of different brokerages or exchanges can essentially occur off-market.
So I'm not buying whatever this is selling.
Side note: I honestly don't understand the popularity of Robinhood. It's amazing how willing many on HN are to castigate ad-supported models and the sale of user data while seemingly at the same time being completely fine with the sale of their order flow.