Pornographic use has long been the "break glass in case of emergency" for the LLM labs when it comes to finances.
My personal opinion is that while smut won't hurt anyone in of itself, LLM smut will have weird and generally negative consequences. As it will be crafted specifically for you on top of the intermittent reinforcement component of LLM generation.
People are already addicted to non-interactive pornography so this is going to be even worse.
While this is a valid take, I feel compelled to point out Chuck Tingle.
The sheer amount and variety of smut books (just books) is vastly larger than anyone wants to realize. We passed the mark decades ago where there is smut available for any and every taste. Like, to the point that even LLMs are going to take a long time to put a dent in the smut market. Humans have been making smut for longer than we've had writing.
But again I don't think you're wrong, but the scale of the problem is way distorted.