I think it's fair to say they were generally recruited via social networks. They knew what RenTec was, they knew someone who worked there (maybe an old grad school colleague or a former student), and when they reached out, RenTec already knew who they were. I don't know of anyone who went there who didn't already have a reputation in academia.
So contrary to astazangasta's original claims, they do seem to me to have something of a monopoly on brains. There are other smart people at other firms, but I don't know of any other place that has such a concentration. (Aside from Jeff Dean's office, I suppose. ;)
I don't work in trading anymore, so I'm not talking my book here. Trading is zero-sum at a transactional level, but has knock on benefits beyond profit and loss:
-Making it easy for companies to raise capital through IPOs or offerings (without a robust secondary market for securities, people will be less likely to invest)
-In commodities: Letting businesses bear the risks they want and insure against the ones that aren't their core business
-Liquid markets let real people trade in and out of investments without friction at fair prices
-Providing accurate price signals to other businesses and the broader economy
So I don't think I was saving the whales, but I don't think it was wasteful, either.
Also, as a mildly clever OCD math guy who's semi-good at writing fast C++ code, I don't think I would have been curing cancer anyway.
ETA: At least in the case of HFT, if you accept that markets need intermediaries of some sort, it seems more efficient to have a few dozen tech/math guys do the same job thousands of guys in mesh vests were doing years ago, and cheaper.
I mean there are computational cancer models that need to be written and optimized.