Admittedly, kind of a dick move, but I have to admit I did find it kind of funny at the time.
To go a step further, sure he killed Dumbledore but without knowing why, and without knowing the real why that's revealed later, only a small part of the fun is lost. That's what makes it re-watchable to me. I'll remember the twists and the endings, but the emotions and the minutae are what keep me watching.
I mean, keep in mind I was fourteen when this happened, and fourteen year old boys are very often assholes and I was sadly not an exception to this.
I guess I just found it funny how much of a reaction people had with it. I liked the Harry Potter books too, I was reading them like every other fourteen year old was, and the plot being spoiled for me didn't really bother me very much, cuz, you know, it's just a book. Some people really got upset.
Again, definitely a dick move to do that, and a dick move for me to find it amusing. Kids are douchebags.
There's entire categories of entertainment media that use "unfortunate things happening to strangers" for comedic effect.
Also, there's the assumption that it was a real spoiler. It's not immediately verifiable. What if people were yelling "Snape kills Harry"? Why did the people in line assume the guy yelling into the night was being truthful, or that weirdly cropped images of pages weren't just photoshopped?
I acknowledge it's a dick move, but it really is just a spoiler for a book, not exactly life ruining and really shouldn't even be day-ruining. I had the book spoiled for me too and it was just something I moved on from, somehow.
This was done because it was the easiest way to massively distribute pain to people about a known weak spot. It was mean spirited, anti-social, and honestly indefensible.
If it isn't what's the defense?
Elsethread, you mention that "some people really got upset.". In some sense, the more upset they get, the more successful the troll and the funnier it gets, right? At least, it feels funny to me, at the same time as it also feels bad to imagine upset kids, at the same time as feeling that upset kids learning that other humans are cruel is a necessary part of growing up.
These were people who lined up for hours outside of a bookstore still waiting to get in after midnight. Many of those people were young and the lack of perspective and experience at young ages often results in assigning a disproportionate weight to the emotional events they experience. An event like that might not have been day-ruining for you, but I have no doubt that there were people who were genuinely hurt by it.
The question of whether humans are more biased towards social or antisocial behavior[1] is a complex one that philosophy has struggled with for a long time without a clear consensus.
1. Often historically framed as whether humans are inherently good or evil.
Assholes do exist, and you should be aware of them, but assholes are a tiny minority of the population. There are far more people who aren't assholes, and an even greater number of people who are just doing their own thing and can't be bothered to go through the effort to hurt others just for kicks.