I agree, AO3 can be a blessing AND a curse. I started reading fanfic when it was only available on fan forums/old style fic archives/Webrings and LiveJournal so I thought AO3 was a great idea until it started going very weird in certain fandoms.
Reading about the idealised relationships in fanfic can be a bit tough at times, but it’s wish fulfilment (just like Mills and Boon can be) and so I don’t read fic when I’m in a bad mood because then it’s likely to exacerbate my grumpiness. Or, if I’m feeling disgruntled, I stick to genfic that concentrates on long complex plots.
I also think that, when it comes to relationships and sex in fic, the male characters in slash pairings wouldn’t be likely to be having the mind-blowing, multi-orgasmic impromptu sex in real life that a lot of these stories always include because that’s more like the sex female bodies have. So it reminds me to feel chuffed that female bodies are capable of great things that male bodies aren’t 😈
I got into fanfic as an adult so I absolutely agree with you that it’s definitely not a healthy thing for teenagers to get into because it can distort their views of adult relationships just as badly as video porn can. Plus, nowadays there’s a lot more activism and ideology involved in fanfic than there was in the past and kids can get sucked into that too before they’re mature enough to understand complex concepts.
Fan spaces can be a bit Lord of the Flies with kids creating their own online societies away from adult supervision (which definitely attracts weirdo men who look for kids to take advantage of). I wish media creators were more mindful of this aspect when trying to generate online buzz or when using social media or when actors are trying to raise their profile by adopting identities and causes.