Disclaimer: I'm not in finance, don't know much about it, but it's what I understood while watching the movie ;)
For example, if we took a simpler example of something more people are familiar with like options...let's say you buy a put at a strike of 100. The stock is trading right around 100. The market tanks like it has been doing and the stock goes down to 80. That's great for you since you had the put. You technically have the right to buy the shares at the market and shove them onto someone and force them to pay you 100. Most of the time, since we're dealing with derivatives, they just trade the value of the option itself and skip dealing with the underlying security because it takes a lot of capital (100 shares * 80 bucks each in this case). So the value of the option (the derivative) should be around $20 as you approach expiration and the premium fades off. If the market maker for the options has way too much exposure and wrote naked puts (meaning they didn't have the underlying security) they took on a ton of risk and basically got fucked. In this scenario it's like Burry calling and finding out his options are worth like $1.50 instead of $20 simply because they are thinly traded and therefore can't get a good price by anyone. This actually happens on some options - you'll see a huge spread between the bid and ask on some options so it's not like it doesn't happen even for this type of retail-friendly derivative.
Yeah, right, it's so nice platforms prevent people from selling, just as the big fish unload their own stocks.
Reality is the regulations on the financial system are a feature. Being able to have charges reversed if I get my card skimmed and someone makes a bunch of charges is a feature. Being able to get my money back if the seller ships me broken goods (or nothing at all) is a feature. Having regulations on banks front-running their customer's transactions is a feature (one that Robinhood unfortunately gets around somehow). Having regulation on securities not being scams is a feature.
As with anything, the answer is sometimes.
You want those rules for your retirement account, because if someone can steal a six figure sum from you instantly with no takebacks, that is bad.
But the overhead of that system is not always required, and it's the major reason that we don't have e.g. micropayments. The overhead of allowing transactions to be reversed eats the entire transaction amount for very small transactions.
So it would be good to have a system where you could, for example, transfer $50 into it from your bank account, wait the month or so until the transaction can no longer be reversed, and then transfer it from there a few pennies at a time with insignificant transaction costs because the small transactions are instantaneous, anonymous and can't be reversed. Which isn't nearly as problematic because even if you get scammed, your loss is limited to the $50 you put in. Instead of getting wiped out, you pay a reasonable cost for a personal lesson on security and trust.
And there is no reason we couldn't have both. Then you keep the bulk of your wealth in the inefficient safe system and some petty cash in the one with lower transaction costs and get the best of both worlds. But the existing rules don't allow that, which is bad.