I hope one day speed of trade execution will depend on beating cancer. Those guys will solve it in a month.
Frankly, "Why aren't you curing cancer instead?" ought to be a recognized logical fallacy.
And I don't get this "our brightest minds wasted on HFT/adclicks/etc" argument. Research positions at universities and labs are extremely competitive. There are hordes of brilliant people beating down the door to work on the problems that matter. The bottleneck is funding. A smart person who chooses to work in a higher-paying field and contributes enough financially may well have a larger impact on overall scientific progress than doing research in person.