I've never/rarely had to actively avoid seeing a spoiler, but yes, I'd rather not know ahead of time what's going to happen if I'm actually going to see the movie. For the same reasons I don't like seeing the same movie twice.. Actually, come to think of it, there is one scenario where a number of times I've avoided reading spoilers: reading about movies on Wikipedia. A lot/most/all of them have full plot summaries on the Wikipedia page.