I think the moralist argument is that the young are more easily influenced. And I understand being disturbed about the content of fantasies, and fiction propping up patriarchy. I'm being disturbed about mine frequently, but personally I think 12-14 is too late to fix in taste what patriarchy already broke.

I mean, when I became a feminist as a teenager I noticed that my fiction reading preferences were not in line with my politics, and I tried to "fix" it, so from maybe 14 to my early twenties I weeded out for ideoloogy, but it didn't work at all. I still find rape and humiliation fantasies hot, and I still like male characters better, and I still have a thing for authoritarian warrior fantasies with obedience to duty, and for glorified violence, and destiny and a natural order in the universe, even though all those ideas are icky.

So basically since I couldn't change my tastes, I decided that it was best to be aware that the ideas are problematic and still enjoy them in fiction. I do think that fiction has a role as subtle (or not so subtle sometimes) propaganda tool, but I think it is not that effective to fix fiction, but that it would be better to fix the root causes and then the fiction tastes reflecting this may follow.