Although this issue has been done to death (though I tend to think the debate has mostly been a matter of people from outside the relevant fandoms saying "Erm, these are totally unencyclopedic" and then the fandoms shouting a lot and getting their way), I'd like to note that the focus on spoiler warnings and on not revealing spoilers in an article is, in a fundamental sense, totally contrary to the process of writing an encyclopedia.
I submit [[Valen]] as the most flagrant current example of this. Valen, for those of you not up on your fandom, is a minor character in the television show Babylon 5. He is most notable for doing a bunch of stuff in the far past before the series starts. Over the first two and a half seasons a bunch of scattered things are revealed about him. Then, in season 3, there's a big reveal where we find out that he's actually a character from the present of the show that travels back in time. It's all very awesome and great.
Here's the problem - the substantive portions of this topic are all things that have to be written from a post-season 3 perspective. There is no good spoiler-free lead for this article. Any lead that attempts to be spoiler-free is, by its nature, going to be a misleading opening. It is impossible to do the job of summarizing the major aspects of the topic and the job of remaining spoiler-free. And as a result, the article is a complete piece of shit. It's not even trying to be an encyclopedia article.
There are other cases like this - [[The Crying Game]] is a travesty of an article because the single most interesting aspect of the movie isn't actually revealed until the sixth paragraph. And there are lots of cases like this. You'd never know [[Sue Dibny]] is a flashpoint for a major debate about women in mainstream comics until you've read half the article. Why? Because it happened in a fairly recent comic, and fans buried it under spoiler warnings.
This is a massive problem. It was one thing when we allowed the use of "spoiler" warnings as a perceived favor to readers. But this is unacceptable - the focus on not revealing spoilers is being used as a pretext to write bad articles. It is clear that the policy of taking care with spoilers and the policy of writing an encyclopedia are, in numerous cases, alien to one another.
Bold proposal: Nuke the spoiler template. Nuke all "spoiler" policies. People may well get burnt on one or two articles they read before they will come to a simple and obvious realization - encyclopedia articles on a topic reveal information about that topic. If you have a desire to not know things about a topic, you probably shouldn't go look it up in an encyclopedia.
This should be obvious. Our mission is to provide information, not hide it.
-Phil