You're right that the original rationale for copyright was the advancement of learning. Of course, human learning had advanced reasonably well in the Renaissance without copyright law, and it continued to advance in the 18 and 19c with much, much shorter copyright terms than now exist. +

So I'm not really very concerned that human learning will grind to a halt—especially since I'm not suggesting any change to the original practice of copyright (which is that you can't reproduce the text of a work), but only suggesting that reading and generalizing from works is non-infringing.