The result was less pressure on the publishing industry to censor books. When Christian activists came knocking, the publishing industry could say, "Look, you guys have an entire section of the bookstore filled with books that cater to your morals. So leave Twilight alone."
I think it's probably time to create a similar genre for leftist activists. A "safe fiction" genre would allow for books that have been stripped of all things leftist activists find offensive. No body shaming, homophobia, mental health related slurs, etc. Having designated "safe fiction" books might have a similar effect of relieving the pressure to make all books "safe" in the eyes of left activists.
Of course, there remains the barrier that most individuals in the publishing industry are hard-core leftists that fervently follow the whims of leftist activists. It's standard these days for books to be edited by "sensitivity readers", who point out all potentially offensive things from a left-wing activist viewpoint, before publishing is permitted. (Source: am deeply involved in the writing and publishing community, and have had many friends go through the sensitivity reading process.)
Shifting away from this mentality is going to take a major push by the reading public, who will need to make it clear that they are not okay with a small minority enforcing their worldview through censorship, regardless of whether the censorship is coming from the right or left wing.