I don't get why the Robinhood apologists pretend that zero commissions are some revolutionary new thing. They're not. Back in 2006 there were already discount brokerages offering zero commissions on stock trades. Zecco offered a limited number of free trades pre-GFC, and so did several other brokers. Furthermore, Robinhood's PR team acting like fractional share trading is some brilliant new innovation is also highly disingenuous. I've been able to trade fractional shares at other brokerages for a long time now. Using the fractional trading point to attack Buffett as a rent-seeking elite is even more absurd, given that Buffett specifically created Berkshire B shares in the mid-1990s to prevent individual investors from getting duped by fee-collecting promoters who were setting up trusts to make BRK fractional interests available to the masses.
The difference between other discount brokerages and Robinhood is qualitative. Other discount brokers offer zero commission trades and fractional trades but don't make use of the gamification elements (flashing lights, Tinder-like swiping when you make a trade, etc.) to the extent that Robinhood does. I've never seen confetti pop up on someone's screen when they make a trade at Fidelity. Saying that people will learn by losing money on Robinhood and "graduating" to more sophisticated investing is a bad argument. It's the equivalent of claiming that a certain amount of people who enter the Vegas casinos will learn from their mistakes and one day study linear algebra and advanced probability theory. It may be true for a vanishingly small part of the population, but it's not the reality for the average person, especially one who is 1-2 years out of high school and who doesn't know any better.
Add in the payment for order flow and the history of questionable moves, like making its users' aggregate trade data publicly available in an API, and it's clear that Robinhood's interests are diametrically opposed to those of the retail investor. That's why Munger and Buffett attack it. Not because it's "innovative" (it's nothing of the sort), but because it's a shady company run by shady people.