YC is directly integrated into the heartbeat of Silicon Valley, gaining more insight into where the puck is going to be, far better than any outsider. If they can match traits of a group/person to an idea only they have the privilege to imagine, you might have a winning combination.
The fact that people are complaining about this likely means it's a good idea, or should at least be tested. Occasionally throwing a monkey wrench into the machine is always good practice.
Colleges do this already by accepting smart students who don't know what to major in yet. Who cares if it takes them some time to figure it out? They're smart! They'll get it!