Quoting Todd Allen toddmallen@gmail.com:
I am not, per se, comparing spoiler warnings to vandalism. I am, however, stating (and will state more clearly here) that just because an option is popular with "the public" doesn't necessarily mean we should actually do it. Many things are popular but outside the scope, mission, and ideal of Wikipedia. That's fine, other sites can handle those. If you want spoiler-free plot summaries, rumors, and speculation, those are very popular. IMDB is a great place for you to look. If you want encyclopedic information, including a summation of the full plot, based on verifiable and sourced information only, that's what we do.
I don't think any of the pro-spoiler people are arguing that we should have spoiler-free plot summaries. The argument is to give a notice when we do have spoilers.