attendant discomforts -- they are many: ask any soldier -- is not, I think, part and parcel of being in harmony with one's script. That their conduct was not conducive to happiness, as they were well aware, is amply proven by the fact that they had to be sneaky, and keep their aims as secret as was feasible, until such was no longer possible. Of course Eru did not intervene. As the creator of them all, in a sense Eru could not intervene. When one's children quarrel, one cannot intervene without taking sides, so to speak. One can only help them pick up the pieces in the aftermath of their dispute, which is what Eru did.

As for bringing them to death: is that a punishment? I don't think so. Death is an ending, of course, and a quite final one; but it is no more a punishment than birth is, under normal circumstances. Indeed, the elves referred to death as the gift of the Second-born. The First-born, the elves, had their lives tied to the rest of creation, and in a way were limited by that. Humans were not, and the gift of death gave an implicit promise of a real immortality, which was not tied to Eru's material creation. True it is, that when one envies another's gifts, one is inclined to downgrade or overlook one's own...