Book Introductions: Do they need to spoil the plot to get their points across?

I'm reading Under the Volcano right now (And not liking it so far) and have had a great portion of the book spoiled. Do you want to know why? It's not because somebody told me about the book and recklessly told me key plot points. It's because I read the introduction, which in itself revealed major plot points to discuss overarching themes and to make comparisons to other work. But why? This is not the first time this has happened to me. In fact, it happens all the time. Whenever a scholarly dissertation is made on a famous story, one thing that usually happens is that the scholar will say, this happens because of this, and this represents, yada, yada, yada, but why is this put at the beginning of the book? I could understand if you've already read the book. But if you haven't, you're basically getting an unasked for Cliffnotes version of the story that you were actually excited to read. Why the hell would they do this?!

I mean, if this content was put in the afterword, then that would make a lot more sense. I mean, NOW you could tell me why this character did this or that since I just finished the book. But by putting all that information in the introduction, it totally destroys any reason to even read the book, other than to understand what the introduction is connecting to the overall content. But that seems so backwards! Why do that?

And I already know what you're saying. You're saying, hey, numbnuts, if you know this is a problem, then why do you read the introduction in the first place? Well, first off, don't call me numbnuts, and secondly, not all introductions are like this. I feel that there are many instances that in order to even understand the book, especially if it's old and has details that wouldn't be understood by a modern audience, then the introduction is necessary. The book It Can't Happen Here, by Sinclair Lewis comes to mind.

In that book, Lewis referenced several political and media figures of that time that I would have no idea about if I didn't read the introduction. Did the writer of that piece spoil some of the key details of the story? Yeah, he did. But I feel that the book would have been incomprehensible, at least from an historical viewpoint, without that insight. So for those kinds of introductions, I don't get TOO upset. But when your introduction mostly reveals plot points of MULTIPLE books to compare it to the book you haven't even read yet (as does the intro for Under the Volcano), well, then you've pissed me off on multiple fronts! Don't do that!

But what are your thoughts on the issue? Do you skip introductions altogether, go back to them once you've finished the book, or read them before the content like I do? I'd like to hear your thoughts, fellow readers. Please leave them in the comments below.