Phil makes some good points but I see them as being about a subset of 'spoiler' articles where the fundamentals of the article are inevitably plot spoilers. For instance, I would include [[The Mousetrap]]: as presently written it necessarily begins in the middle, without a proper introduction, but try to write it properly: "The Mousetrap is a murder mystery play by Agatha Christie which is notable for its plot twist in which the murderer is revealed to be the police sergeant sent to carry out the investigation" and it's a spoiler from the very first lines.
Spoiler templates are overused but getting rid of all of them is too extreme. Perhaps only really vital plot twists should be covered? Meanwhile the idea of a foldable spoiler warning for articles in the class of 'the whole thing is a spoiler' is worth trying.