Re: The problem of Sansa Stark
For those who are not familiar with Game of Thrones, Sansa Stark was a young girl separated from her family and surrounded by political enemies for books 2-4, and yet somehow, she managed to get through that situation nearly unscathed. Something about her drew protectors to her, so she was shielded from some of the worst potential side effects of what could happen to her. In other words, by the time you reach the end of the 5th book, she's never been raped (just stripped half-naked and beaten one time and married off against her will to a husband who was honorable enough not to touch her). Characters joke that there's no way a woman in her situation can 'still be a maid,' but...the readers know she is.
In the films, they tell Sansa's story more or less how it was written. The books end with her in the Vale under the dubious protection of Littlefinger. The TV show gets to that point...and then Littlefinger marries her off to the Boltons.
In the books, Ramsey Bolton (Roose Bolton's naturalized bastard son and quite possibly the worst person in a cast containing many horrible people and a few other psychopaths) does indeed marry 'Arya Stark' (Jeyne Poole being passed off as Arya Stark), and the other characters react as if one of the Stark girls is in Winterfell.
So, clearly, the TV show decided to replace Jeyne Poole (Sansa's very minor character friend from 5 seasons ago) with Sansa herself. Since this role required an innocent young woman to be raped and brutalized by a particularly vicious man, there was an understandable up-in-arms reaction from the fans who rightly pointed out that book!Sansa had never been raped or used in this manner. The scene is in the book...it just happened to someone else, not Sansa.
Here's the thing, though....the books obviously have to be setting things up, and getting Sansa to the North (eventually) is something that has to happen. Granted, they could have done the whole 'Arya' ruse, and then, just kidding! and then moved on to the plotline which would bring Sansa and the knights of the Vale to Winterfell by some other means. Certainly, the TV show *could* have done that. The TV show is also trying to end the story in eight seasons. They really had to accelerate the plot, and that did mean doing disservice to certain characters and plotlines (such as the Sand Snakes). Season 6 has some very uneven writing (vigorously anti-magic Ser Davos' surprising suggestion to attempt to resurrect Jon Snow, a man he barely knows, immediately after the death of King Stannis, a man he's served his whole life -- what??), and it's clear they've gone 'off script' and run out of book material to use.
The question to ask is...what is the purpose of tormenting Jeyne Poole in this way? The answer is that it outrages everyone because they think that the Boltons have taken a Stark girl hostage. GRRM could play coy with his story - write about tormenting/raping a 'fake' Stark girl, while the actual Stark girls remained unmolested. But...was there any need for a fake Stark girl in Winterfell? And all the outrage over Sansa being treated that way only proves the point that no one cared about poor little Jeyne Poole who had no choice in the matter and was forced to impersonate Arya and go through with an awful marriage to the worst man in the world. CLEARLY, the audience cared more about this happening to Sansa than to some random nobody. It's not fair that she escapes Joffrey only to fall into Ramsey Bolton's clutches! Well, true, but since when is anything in this story or world remotely fair? The story is almost entirely about the worst possible thing happening to almost everyone. People can be upset, but have they seen this show?
So, while I realize my opinion is unpopular, I do assert that the show's writers absolutely made the right choice to use Sansa Stark in the role of 'Jeyne Poole pretending to be Arya Stark.' And not showing the wedding night on screen was one of the few times Game of Thrones cameras have shown *any* discretion; I for one appreciated that. By not showing her nudity, it made the scene entirely about her fear and pain. They also did not make the violence done to her meaningless, but used it as part of her story and the end of any trust she might have had for Littlefinger. It informed her decisions moving forward - her acceptance of Brienne, being the person to put an end to Ramsay, her reluctance to call on the knights of the Vale, her arguments with Jon. In other words, they integrated Sansa's time as 'Lady Bolton' into the story and made sense of it with her story. It remains to be seen how it will impact the final season or the end of Sansa's story (perhaps she'll never marry again?), but it was not in and of itself a bad choice on the part of the show's writers. Unpopular, sure, but not bad.
Now the superfluous use of the Sand Snakes, on the other hand.....
All that being said, we're not writing Game of Thrones. We're not going for shock value or gross-out or any of that. We're not trying to prove how 'gritty' and 'realistic' our fantasy world is by making it as vulgar as possible. We aren't creating a society where fighting men travel around and think they can do as they like because no one is there to stop them. Even the least honorable elves have a lot more honor than your average character in Game of Thrones. AND...our source material is already as written as it's going to be. It's not like we need to invent an ending for the Silmarillion - we know who lives, who dies, and who tells the story!
Subtracting out minor characters is not uncommon in adaptations. One can either give their lines/roles to more important characters, or replace them with a mere device to accomplish the plot that they are meant to be responsible for. And so, while we might get upset that Radagast did not appear in Peter Jackson's The Lord of the Rings, his role in the story is covered by the moth that Gandalf uses to communicate with the eagles. Frodo does not have his dreams in the House of Tom Bombadil, but Gandalf does tell Pippin of the 'far green country under a swift sunrise.' The minor characters are subtracted, but not everything from their stories are lost.
What we are faced with here is something different. We are told this happens, in the 'plot summary' version of the Quenta Silmarillion. We are not told who it happens to. Some elves are made captive. Some escape. Some are compromised by Morgoth and then let go. Eventually, the Elves learn not to trust former captives, because they *might* be compromised. So...we can either make this happen to a named character whose story it 'fits' into, or we can invent a character for this to happen to. There is no minor character to replace; it's an unnamed character's role in the first place.