RenTech doesn't do "nothing". They do a ton of research and write a lot of code. Then, they purchase securities from people who want to sell them, and sell them

RenTech doesn't do "nothing". They do a ton of research and write a lot of code. Then, they purchase securities from people who want to sell them, and sell them to people who want to buy them. Why is this more palatable if there is a trader in between?