While I’m old school and a huge believer in “don’t like, don’t read,” there are caveats to that. Firstly that you tag stuff, so people know if the thing that they don’t like is in your fic, and thus know to avoid it.
But secondly I will always have deeper issues with the argument “It’s fiction! It’s not that I ACTUALLY condone rape/incest/abuse/child porn!” Because if you are framing any of those things in a sexy or romantic light, people will internalize that. You may actually be doing it yourself, and you just don’t want to admit it because simultaneously you know that it’s a Bad Thing in real life.
But the point is, humans are not hatched fully-grown and with complete knowledge of what is and is not good for them. These are things humans learn. They learn these things through human interaction and through the consumption of media. If you understand the importance of representation, you understand the influence of narratives and media.
So you want to write stories about fathers raping their sons, and you wanna present it as sexy and desirable, you need to be prepared for the damage it can do. (And before anyone tries to tell me I’m exaggerating with my example, I walked out of a panel at a convention because the panelists and audience members were happily gushing about that very subject and how hot it is). Your excuse of it being fiction is a weak one, because you are romanticizing something, which can not only normalize it but also mislead people into thinking it’s a good thing. Like with inexplicableshame’s personal experience. Or like how people who didn’t know better thought Bella and Edward had an ideal relationship. Or how people who don’t know better think 50 Shades is hot BDSM and something to want for themselves, instead of realizing it’s not BDSM but obsessiveness and abuse and something to be avoided at all costs.
Everyone doesn’t magically know better.
Depicting the aforementioned subjects as anything other than what they truly are (reprehensible and traumatizing) can and will be seen by some as endorsement.