Earlier quoted context omitted.
A nice thing about being a big, reputable brokerage is that you have access to big, reputable piles of cash to cover clearing collateral.
A casino definitely can't shut down a blackjack game in the middle. That is not true. What are you even arguing here? That the purpose of a brokerage is to take customers money and play weird games with it to maximize profits and is allowed to just not have enough money to cover all cash purchases? That is like if a bank just didn't let customers withdraw their money, and kept operating like nothing was wrong. Clearl…
I don't think this is at all like a bank that won't let you withdraw your money. I think it's like a brokerage that has to post 100% collateral --- out of their money --- for every share of GME that you ask it to buy, doesn't have the money to post that collateral, and thus can't buy any more GME for you.