The philosopher goes back to the cave, not because he is benevolent or generous, and not because he pities those who stayed inside. He goes back because he HAS to. Not by logically following out the consequences of beholding the GOOD, but in the way that ANY philosopher is familiar with: that necessity every philosopher experiences: to write, to talk.
And this is what is mysterious: the philosophical Eros that turns backwards: the one that is not looking in the direction of the truth, but in the direction of the notebook and of human confusions.