[Firefoot]

This is either despair on an unimaginable level, or its a final, desperate attempt to impose meaning on horror.

I do not agree with either of these two points. Like Child, I believe that Frodo had some hope, hope of peace and healing. Despair is only for those who have no hope. On the same lines, if Frodo had hope, then there would not be that horror, because Frodo did not utterly lose everything because he had hope.

Frodo could not have known what he would go through when he volunteered to take the Ring in Rivendell. He might have had some sketchy idea, but he still believed that he would be able to go home and live in the Shire in peace when it was all over. Had he known what he would go through, perhaps he would be in somewhat of the same situation as Merry and Pippin as Gandalf describes for Elrond:

It is true that if these hobbits understood the danger, they would not dare to go. But they would still wish to go, or wish that they dared and be shamed and unhappy.

Not exactly the same, but rather than 'danger' perhaps 'sacrifice'. It still doesn't go just right, but generally makes my point.

But the point is that even though Frodo did not realize it at first, he changed; realized the sacrifice that he would have to pay for the world to be saved. I believe he understood this, at least to a small point, when they realized there would not be enough food for them to get back. There could be no going back. Frodo and Sam had plenty of options to turn back, but they didn't, even realizing full well that if they didn't, they wouldn't go back. There came a point when they figured their task was to accomplish the Quest and die. But even in this, I believe Frodo had hope - not for himself, but for the whole of Middle-earth: that if he could cast the Ring away then the world would be saved. He accepted his task just the same when he was in Mordor as he did in Rivendell.

Or perhaps it was only afterward, when it was all over, that he could say, 'OK, I was forced into it, I have had everything that matters to me snatched away, & I'm left with this hole in me which is going to swallow me up, but I can now see it was worth it'

Frodo wasn't forced into it though. He was willing to make the sacrifice. At the end he suffered devastating loss and pain, but he did see that it had been worth it.

"But," said Sam, and tears started in his eyes, " I thought you were going to enjoy the Shire, too, for years and years, after all you have done."
"So I thought too, once. But I have been too deeply hurt, Sam. I tried to save the Shire, and it has been saved, but not for me. It must often be so, Sam, when things are in danger: some one has to give them up, lose them, so that otherrs may keep them.

It seems that Frodo was very accepting of his loss, and I believe that this is for two reasons: that he was able to see the Shire and Sam safe and in peace, and because he had hope that there still might be peace and healing for himself in some way.