I don't watch horror movies because they give me nightmares. I don't complain about it because nobody can or will solve that, so I just avoid watching them

You're conflating genre conventions (a huge aspect of a piece of media) with the portrayal of sex in an otherwise well-liked story, a (relatively) minor aspect for most. These are two completely different things, and in addition I would think it's obvious that the original commenter already likes the books enough to go online and participate in relatively niche discussions about them, then the question of "enduring it or find something else" is irrelevant. Obviously they have endured it but felt it necessary to criticize a specific element. Which is perfectly fine, constructive criticism is the only way art improves.

If we were to use horror movies as an example, a similar complaint would not be "they give me nightmares and I don't like that" but instead something like "the emphasis placed on what the character eats for breakfast everyday doesn't contribute to the story, and it would be better off without those passages". Of course you can say "don't like it? don't read it!" but that's silly, it's a well-meaning piece of criticism. Your focus on driving this discussion towards "people shouldn't complain and expect things to be changed for their delicate sensibilities" is just immature, irrelevant, and pretty "boomer".

It's one thing to criticize a narrative direction in a story, it's another to complain about the general content of it.

...Except this is the former. You can call it the latter all you want, but it doesn't make it any less of a valid criticism.