G'day Steve,
<snip: why don't spoilers ever generate complaints?/>
Conjecture isn't necessarily fallacious. We are all, most of us, readers as well as editors. The people who like spoiler warnings and argue for their retention are all, presumably, people who appreciate spoiler warnings in the text they read. The set of people who appreciate them (and would mourn their passing) is clearly not empty.
People don't always write what they would like to read. Sad but true.
Witness, for example, the endless trivia and "in popular culture" sections. Now, finding out at [[Jupiter]] that the megahit game [[Bug-Eyed Space Invaders With Halos Doing Moon Jumps]] was set nearby may be of interest to two or three idiots who otherwise wouldn't care a jot for the planet, but the vast majority of stuff we see in such sections is asinine ([[Statue of Liberty]] used to --- maybe still does --- have a pop culture section longer than the rest of the article, containing such gems as "The Statue featured in one Simpsons episode, where Bart shouts at some immigrants, 'Go home, the country's full!'").
As a reader --- let alone my concerns as a Wikipedia editor, and therefore self-appointed co-guardian of its content and reputation --- some pop culture sections are simply horrifying. I understand it's the same for the vast majority of readers who read it. The support of such sections is that they provide an outlet for, for example, newbies who feel they want to contribute, and say, "Hey! I saw this statue on /The Simpsons/! I don't know what it's for, but I remember a funny joke about it ..."
Parts of Wikipedia, great swathes of it (see also, stub-sorting, certain infoboxen) are not there for the benefit of readers. In many cases, they exist because someone wants to write them, and doesn't give a damn whether anyone would want to read them.