Originally Posted by MigueldaRican
That's a little more detailed than the criticisms I've read. On theonering.com's "list of changes" website, the criticism was that Sebastian seemed too contemporary. They acknowledged the fact that Tolkien used contemporary (rather fratboyish sounding) names for the Orcs, but said that Tolkien regretted that. My first response to that is, "Too bad." It's published.
But even if that's the case, the nitpicker's response would be: well at least the Orcs are more forgettable characters individually. Fair enough. But that doesn't exempt other characters of the books: Tom Bombadil, Rose (Rosie), Bill. And let's not forget the name Fatty.
Still even at that, those characters aren't exactly main characters, though (at least in the books) Tom's part is bigger. But it's not like they were the principles of the books. Imagine if one of the Nine were just named Jackson or Brian. The thing about Sebastian is that he's thankfully a very minor, forgettable character.
Sebastien is not a modern name.
(I think they meant "modern" rather than "contemporary", as that would imply it fitted in with the era of the setting very well.) But nevertheless, it is out of place.
On the Orc-names, the only ones I can recall were simply in English, so presumably in-Universe it is simply something in the common tongue but they seemed to suit the characters quite well. What he regretted was making everything about them seem irredeemably evil.
You have to remember that Tolkien was a linguist, and liked making up languages and sounds, but also felt that it wouldn't do to overload his audience with his own musings. So some names are supposed to be translations into English from whichever language (Westron or Hobbitish or what have you)Tolkien used, to fit with the specific cultural feeling he had decided upon.
But of the four other examples that you picked, only one is inexcusable: Tom Bombadil, "Tom" being Aramaic/Hebraic is not a valid origin for a name as laid out by Tolkien's own rules. However, he is excused by the fact that he was actually a character from stories entirely unrelated to LotR which Tolkien wrote before, and then decided just to stick Tom in there.
The other three you picked: Rosie, Bill and Fatty. I don't see what the problem is with Rose - if you call someone after an actual noun in your native tongue, you expect it to sound consistent with the rest of it. In the Shire, they would name girls after flowers in their own tongue, so naturally in English this would be translated. Otherwise we'd have random, harsh sounding names in amongst the English (Tolkien devised a little of the language for Hobbits, thus any noun-names he might give characters would remain in English). Hobbits are meant to sound "Englishy" and Englishy they sound.
Thus it is with Bill and Fatty. Bill being the diminutive of William, being derived from Wilhelm, is decidedly Germanic, thus in-Universe exists as a completely different sounding name which happens to have similar origins to William. Fatty is a nickname, just like any other nickname, I don't see a problem here either. I'm sure the even Ancient Greek civilisation had a derisive term of endearment for those with girth problems. But I'll go further, by reminding you that Fatty's actual name was Fredegar, which is another Germanic name, thus it falls under the branch of "names Tolkien used to fit with the specific cultural feeling he had decided upon".
In both The Hobbit and The Lord of the Rings we start off in the Shire. That is "home", and should feel familiar. Thus we get names that you might find in our world. As you leave the Shire you get further from home and the setting altogether less familiar(this is more pronounced in The Lord of The Rings). Thus you start off meeting Tom Bombadil or a troll named Bill, but then you meet a cave-dweller named Gollum or a Ranger named Aragorn and home feels further away.