Meta: What Factors make James/Lily/Snape such heated and intense topic?
Source: What factors makee James/Lily/Snape such a heated and intense topic?
The real problem, I think, is that Rowling was always writing detective fiction, even in the Potterverse. Characters make statements which turn out not to be true, and we are deliberately misled in order to set up sudden dramatic reversals.
Snape is a hugely important character, in many ways the backbone of the plot. If he hadn't first relayed the prophecy, then begged for Lily's life, there would have been no blood protection on Harry. The Potters would probably still have been killed, just because they were Order members, Harry would have died a baby and Voldemort would have won. So he is very important to the plot, yet Rowling wished to mislead us about his true role, in order to set up a coup de theatre in the final book.
In addition, he was based on her mother's friend and employer John Nettleship, in whose office the young Rowling spent several years' worth of coffee breaks, and with whom she seems to be a bit obsessed, We know more about Snape's background than that of any other characters except Harry, Dumbledore and the Weasleys. His gestures are minutely described - how he walks, how he moves his hands, how he moves his lips, his expression - yet we only see him from the outside. We have to work out what is going on with him by observing his gestures, which are tells. This makes him seem more vividly real than most of the characters, because we see and learn him the way we see and learn some real bloke we met in the pub.
Yet, we are deliberately misled into thinking he's going to be a villain, and many people fell for it. By making Snape seem to be a villain, we are initially misled into thinking his dislike of James and Sirius was just bias.
The initial impression we are given of Snape and his relationship with the Marauders is almost wholly misleading, and is meant to be. Rowling is playing mind-fuck. Yet, the author's pen lingers over Snape's every gesture so lovingly that it's clear he's important to the plot, and he became the epicentre of many fan theories and of a host of fanons - ideas made up by the fen and then treated as canon.
When Rowling suddenly sprung it on us that James really was a bully, and later that Snape was a (slightly tattered) hero, many people were reluctant to give up their deeply-held fanons which had shaped their understanding of the books, and tried to force the text to fit the fanon - so we get people who still refuse to accept that James bullied Snape, regardless of what Rowling may say both in the books and on Pottermore.
Something similar happened with Dumbledore. Some people still clung to their idea of him as a saintly, kindly old grandfather figure against all the evidence, while others were so shocked by the revelations in DH that they decided he was a complete villain with no redeeming features.
Also, many people on both sides of the debate can't cope with the idea that somebody can be both a self-sacrificing hero and a pain in the arse, so depending on which side they're on they deny either Snape or James their heroism.
The films are an added complication. Lily in the books is brave and witty but a bit nasty (OK, Rowling seems to like her - but Rowling too is a bit nasty), but people confuse book Lily with the be-haloed Saint Lily of the films, and they muddle book Snape with film Snape. Rickman!Snape is more romantic than book Snape, who is a bad-tempered, scruffy, rather ugly little pinsaw. But Rickman!Snape portrays Snape as a calm, confidant, middle-aged bully who slaps students around and punishes Harry for successful Legilimency, and who ignores a live baby in order to cradle a dead woman. Book Snape is not much older than the students, tired and stressed but very non-physical, and he praises Harry for breaking into his mind, and always protects the children.
So then you get people muddling the books with the films, and saying that book!Snape is evil because he ignored a live baby to cradle a dead woman, even though that didn't happen in the books (and even in the films, he couldn't *know* Lily was dead until he'd examined her, and if she'd been alive but unconscious she would have been in more need of attention than Harry), and also forgetting that Snape was only twenty-one when Lily died.
On top of that, you get a lot of teenage fen who impose an overheated, Twilight-derived sensibility onto the books. James and Lily can't just be two twenty-year-olds with a baby - they have to be an ideal couple, or a horrible one. Or Sev and Lily have to be an ideal couple split up by wicked James, or alternatively Sev has to be a stalker who was friendzoned, even though in the books there's no evidence that Lily ever fancied Sev and very little that he ever fancied her, and when she told him to go, he seems to have gone, and stayed gone. Snape's continuing devotion to Lily has to be primarily sexual, according to this section of the fandom, even though there's no evidence that it was in the books.
Then you have to consider that most Potter fen are women, and women tend to identify with the character who suffers most. That tends to be seen as either Snape or Sirius, so you have people passionately devoted to one or other of two characters who are enemies.
Because Snape is both very vivid, and suffers a lot, and has this uber-romantic "secret hero" thing going on, his fen are especially passionate. I've been active in fandom since 1981 and I have never known a character be loved as deeply by as many people as Snape is loved. And of course those of us who love Snape are irritated by the fact that so many of the people who dislike Snape, dislike him on the basis of things which only happened in the films, or which didn't happen at all, except in fanon - such as the oft' repeated claim that he was biased against Gryffindor, even though he only made one disparaging remark about Gryffindor in the entire series, when he was eleven. Disliking a character for things they actually did is a matter of taste - disliking them for things you made up, and then presenting that as canon evidence, is infuriating, whether it's applied to Snape or to Dumbledore.
Addendum: another thing which infuriates many Snape fen, especially me, is the double standards which are applied to Snape, so that he alone is judged for behaviour which is normal to his culture, while other characters get away with far worse. For example Snape over-reacting to Harry’s bad behaviour and taking too many points off him because of his resemblance to James is presented as a heinous crime, while Hagrid violently attacking a terrified, cowering Muggle child because that child’s father made a rude remark about Dumbledore is jolly good fun. This is partly because Snape is nasty to Harry while the other characters are mainly nasty to people Harry doesn’t care about, and many readers can’t get beyond Harry’s viewpoint; but it’s also, again, because Snape is written so vividly. Snape feels real, so his faults are treated as the faults of a real person, while the other characters feel a bit cartoony and their often much greater faults are treated like the faults of Tom and Jerry.
