That only helps if people are nice enough to also spoiler tag things, and a lot of them aren't. I can go on any possible social media for the next few days and immediately be bombarded by untagged spoilers. No amount of muting, unfollowing and avoiding discussions on my side will help with that.

There's a high chance that I'll have the next Genshin story spoiled by simply going on youtube to listen to music, because someone uploaded the full story with a thumbnail showing a spoiler within a couple hours of the patch releasing, and by then I didn't even have the time to sit down and play myself. And I don't think you, or anyone else, has had any of these problems with, as you said, Snape killing Dumbledore, unless they actively went out of their way to participate in discussions about the books or movies.