The letter we're discussing was written shortly after the book was published.
If you agree that the letters don't contradict the text then I'm afraid I don't get your point.
Tolkien is expounding on his own work and characters he created. You seem to want to disallow this because it was only in a letter. You also seem to be holding out hope that there is a letter where Tolkien, absolves, I guess,
Gollum of responsibility? You cannot seem to accept what Tolkien said, outside the book, of his own characters and work. If so, that's just very odd to me. Because the book does not justify what Gollum does either. He ends up a full-on villain.
For the record, here is the note by Carpenter before the letter (#181), published in 1956:
I believe I've already mentioned these but here goes again:
Frodo offers
the Ring to
Gandalf,
Aragorn and
Galadriel. None of them have any compunction to strike Frodo dead.
Sam gives Frodo the Ring back after he rescues him but first suggests he might carry it a bit longer. Frodo doesn't try to throttle Sam for even saying such a thing, though he does get angry. Sam doesn't try to kill Frodo for wanting the Ring back. Also, Frodo shows mercy towards Gollum while he has the Ring. Back in
The Hobbit,
Bilbo doesn't run Gollum through, even when he has a legitimate reason for doing so. If the Ring were so pernicious, why didn't it influence Bilbo to do just that, especially when one might normally see the need to anyway? If Bilbo were so inclined and where he might see a need, the Ring might incline him even further, by your argument. But he chooses instead to leap over Gollum, a move that very well might not succeed, instead of running Gollum through. So, I continue to wonder, how can you argue that the Ring turns people into homicidal maniacs when this is demonstrably not true?
Well, it's a nice find for him, as he sees it. And 'gloating' is not some unpardonable find. I'm not sure how Bilbo finding the Ring applies. It certainly doesn't make Bilbo into a murderer.
It's possible
Boromir would have killed Frodo. It's also possible he would have just relieved him of the burden; there's certainly no reason Boromir would need to kill Frodo to get the Ring. But, in any case, rather than for selfish reasons, Boromir is desperate to save his homeland and momentarily loses his faculties. But he is shortly thereafter very rueful of his behavior. The Ring is definitely a very dangerous thing around certain personality types. I'm not excusing Boromir for his behavior, by the way, I'm simply saying his motives were different from Gollum's (also, incidentally, this encounter proves necessary for the Quest).
I'm responding to this post as I go through it rather than read it first, so I'm coming across incidents I've already mentioned. Anyway, you're listing points that seem to argue against your point. Frodo gets angry, yes, but he doesn't so much as raise a hand towards Sam. Gollum
strangles his cousin without even trying to wrest it from him first. This is noteworthy, because Tolkien
could have written it that Gollum accidentally killed his cousin, thereby widening the possibility of redemption. But he chose to go with what he did, probably based on how he'd already written the character.
Frodo is at the very end of his endurance, underfed and under-watered. If he were to have any chance to throw the Ring into the fire it would, very understandably (by any rational person) ,have been gone by then. This does not justify Gollum's murder and attempted murders (nor any of the other things he did in the past, including very likely taking babies from their cribs).
As demonstrated, they do.