Well, in reality people can turn into targets of hate almost as fast as here. Not magically, not really this suddenly, and not for no mundane pretense, but it happens. Typically these sudden explosions of hate follow the revelations of some secret crime or corruption, so how would you think about your previous relationship if it came out that your best friend had been, all along, yes-really, the worst sort of person? Like a child molester or something, and you'd never known?
Typically when close relationships get turned like this, there's a sense of betrayal felt by the non-hated-one. How could they have dared to act so innocent when they were really so vile?! That's even worse than being open about it, right? Sinister, infiltrating, poisonous.
And of course if you DON'T express some sort of feeling like this, you'll be viewed by others as a sympathizer at best, so if you don't want to meet the same fate but also don't want to think of yourself as a self-serving coward, it's best to convince yourself to feel sincerely that you were deceived and betrayed; something like that. And, of course, that may in fact be true!
(It occurs to me that the Etalarche curse is probably markedly superior to organic hate-mobbing because it keeps the targeting narrow: as far as we've seen, there's no risk of the affected Alds turning on each other for not expressing their hate vigorously enough and so being Roger Foi-Hellick Sympathizers who deserve to be torn to bits just as much as he does. While that would probably be more complete in stamping out a movement, it's probably too risky in terms of collateral damage.)