One of the most important social structures of modern society is the corporation - a framework for large groups of people to band together and get absolutely huge projects done. In this framework, the structure itself is more important than individual excellence at most levels. To a lesser extent, the same applies to academia and even "society as a whole".

In that context, I think preferring negative selection to positive makes sense: a genius data-entry clerk is less helpful than an insubordinate data-entry clerk is disruptive.

And remember that we have side routes so real geniuses (of some kinds) can still make it: set up their own company, start their own political party, start publishing their work online, design games in their basement, and so on.