I'm assuming you read it, so why does Harry Potter (a 11 year old in 1991/1992) think polyamory might (or probably would be, looking at the text right now) be a good idea in a future where people live a long time, in said fanfic? I think it's pretty dubious, but the other 11 and 12 year old girls in the same fanfic also seem to be fans of the idea of yaoi like situations, so all semblances of actual historical events are probably gone at that point. This is the UK in 1992, not the US West Coast. To give my personal impression, when I read some science fiction that had some suggestions of polyamory in it in a similar situation, I did not think it was a good idea. I know the whole thing is essentially a morality story and for various plot and author-community communication reasons the "Harry Potter" in the story does not behave like J. K. Rowling's Harry Potter with different adoptive parents nor like any person, child or otherwise, could behave in 1991 and 1992 within the realm of probability, but I think the whole thing could be done a lot better even given the various constraints. How about he actually does science experiments for more than two chapters instead of going on stupid adventures that should probably be left to the JKR books. Cut the time travel as well, figure out some other reason for constraint solving to show up.
Yes, spoilers though, but I don't actually think that explains it. Are there any indications in cannon that Tom Riddle was ever interested in polyamory? I'm pretty sure voldemort is not interested in other people at all after his soul gets all divided, but I don't know about before that. Riddle is not from the US west coast either, so it's kind of dubious.
I don't think the story is trying to take the characters from cannon, but take the world and completely reimagine the characters. The original characters just serve as foils for their reimagined versions. I never really understood complaints about fanfic authors not sticking to cannon character traits. Isn't the point to create new stories that are loosely linked to the original? Anyway, HPMOR is more pop philosophy novel/religious text that attaches itself to a well known world for publicity than any traditional sort of fan fiction.
I guess so. As I said before it's essentially a morality story, but in that sense I think it's evidence for the author having a bias toward polyamory, because there's very little or no in-universe reasons, and there's no broad social acceptance problem in not having polyamory mentioned at all. As an example, I think there would be social acceptance problems if the story had no women or clothing in it. Polyamory is no where near that level.
