Envious bullshit! The reason they are so profitable is that believe it or not they are replacing earlier operators who were less efficient and taking more transactions costs out of the system before. To be anti-Jane Street is the same as being pro-Big Bank of the past, that was taking more money out of the economy doing a worse job!
Unless you know the history of global financial markets and lived it then you don’t understand. For example in the late 80s the CBOT treasury bond bit had over 1000 traders in that pit. They were all making money and quite a few a huge amount. And there was many more people supporting those traders of the floor. That was just a single futures bond contract! With Jane Street we have 2,631 employees doing the equivalent job globally and for less total cost of at least 80,000 employees in late 80s.
The profits per employee are higher obviously but that’s the effect of technology and productivity but the total price being charged to the economy as a whole is much lower. This trend will continue and I would not be surprised in 10 years that a company of 200 people will provide the entire function of those 2600 today, and probably the profits per employee will be $10M per person. But that’s what we want, is a good thing not bad, portraying otherwise is just Envy.