Fanon is nice to an extend..but it's reposted so much I think they believe it's legit, like that it actually happends in game. Every single Sans comic about it has it, instead of the fact Sans actually doesn't know anything, hence the password with the silver key. LIke one or two comics is interesting but....50 of the same plot over and over....
And I've seen it with other stuff...shows or games that people take speculation too far and even attack others that disagree or see it 100% what really happends in game, which is silly, but..you know people. Just like...FNaF, SU, even MLP like...eugh, all that stuff becomes really poisoning.
My biggest fear in non important stuff is that the fandom might ruin Undertale with unecessary angst or so, just as how other games or shows were seen in bad eyes and infamous just due to the fandom. Some prevail in good eyes like Sonic (Well...they do say the games are terrible, the new ones but that's aside of the fandom), but not of them are lucky and just..disregarded like "No, this sucks because people make me hate it". I hope it doesn't happen, please no.