At some level I think that this is about the potential problems inherent in a society accepting the truth of our objective reality, and embracing the philosophy of existentialism (at least in its least systematized forms). Mishima seems to be suggesting that not only will children be unable to grow up properly - or morally - in a world free of the goals and rules of tradition, but he seems to suggest that even many adults will have similar problems. And though it is implicit, he seems to suggest that society needs its old myths. At least I think he does
On the level of narrative, I must say that I really like how the second act of violence is treated completely the opposite of the first act of violence and that, even though I was not enjoying the book at times, this is quite the aesthetic accomplishment.