It's situational. In the topic where this came up, Arale brought up the example of mystery novels, and in that case... yeah, spoilers are evil, because the whole point of the mystery genre is to have fun seeing if you can solve the mystery when (or before) the detective does and how your reasoning stacks up with his.
There is no point doing such a thing if you already go in knowing that the ghost is really Old Man Jenkins. In that case you're literally ruining the entire point of the experience.
Earlier in this topic someone brought up exploration games, and I agree with that as well... as much as I wanted to, I never did watch Lets Plays of Metroid Prime II, Zero Mission or Fusion before playing the games proper because half the fun of a series like Metroid is seeing how much you can find on your own. In a similar vein, a game like Myst (or even Space Quest) is all about challenging your own mind's puzzle-solving and intuitive ability. What even is the point of them, if you go in already knowing how to solve every puzzle or where every Energy Tank is?
It actually does kinda damage the games too, as suddenly interesting design choices and architecture and things that MIGHT JUST be meaningful... are window dressing you barely notice because the guide told you there's nothing there and you should just move on.
.... But then, there's games like Mega Man. Sure, a lot of them try to have a plot twist
It's always Dr. Wily, even when it starts out looking like its someone else.
But I doubt anyone would care if you went in telling them that.
Likewise, if I told you that in Zelda: Ocarina of Time that young Link
eventually gets aged up and sent seven years into the future
would it really bother you?
The latter leads to kind of another thing. Sometimes forewarned is forearmed in a gameplay sense, like some games with a time travel mechanic do this thing where you can grab multiple copies of an item if you get it in the future, then the slightly less future, then the present, then the past... all the way back to its origin, so if you first saw it in the past and got it immediately you screwed yourself. So sometimes its nice to know in advance whether you're playing one of those games or not. For those wondering about Ocarina of Time by the way:
its not one of those games. Once you grab a heart container in the future, its gone in the past too. So grab stuff as soon as you see it.
Likewise, sometimes I get bummed out when I play a game, save, then realize I crossed a point of no return and am now in deep doo-doo. Spoiler for near the end of Earthbound:
Do NOT save after using the Phase Distorter. There is no way to return to the regular world and thus stock up on supplies, and once you've used the Phase Distorter you're basically on your way to the final confrontation with Giygas.
I've also sometimes felt that I didn't hate Metal Gear Solid 2 as much as most people because I went in knowing about how it features the series' most hated character and... thus, I actually was prepared and ironically wound up liking both him and the game. It's weird like that.
But for the most part, I like to play it safe and go in blind if its a thing I'm interested in, which is why I've avoided watching videos about Silent Hill 3 and 4 for a long time now.
But yeah, spoiling just because you don't care and think nobody else should is just the kind of thing an emo thirteen-year-old would do. Imagine someone thinking "I don't care about human life and so you shouldn't either" and deciding to make you not care by murdering your entire family. Okay, that may be an exaggerated comparison, but as they say, in for a penny, in for a pound (and I would almost like to do exactly that to people who think their views should be everyone else's).
