Well, I think the whole thing is pretty simple, really. I'm another one who doesn't really mind being spoiled that much (unless it's some massive plot twist that should be kept secret). That being said, you can never be "unspoiled" -- once a show is ruined for you, there's no turning back. So, it's easier for those of us who want to be spoiled to go through a bit of extra effort than than to risk ruining it for people who want the anime to surprise them at every twist and turn. It probably sounds trite, but this really is one of those "for the greater good" things. A minor inconvenience for some, but it allows us to host a larger, more diverse community. Life is full of these sorts of compromises.
And, to be clear, spoilers are allowed on these boards, but, as Daniel E. said, they have to be in the proper places. If you want to talk about things that happen in the manga, do it in the manga thread. It's not hard. The idea is that people should be allowed to carry on a conversation with people with their same level of exposure to the property. And if you know something that other viewers don't because you've spoiled yourself, you're not doing the less-exposed any favours by telling them what happens next. They're not going to be "blessed" by your spoilers, just because you really really want to talk about it. That being said, I can totally relate to the frustration, as someone who sometimes is more-or-less fluent in the source material for the some of these shows.
Anyway, implementation details not withstanding (the policy itself is a "living document" that's always subject to review and change based on everyone's feedback), the idea of having some sort of spoiler policy is, as Cats said, pretty much unavoidable. And I personally prefer to have something that's pretty clear (even if it is a bit on the harsh side), rather than something vague and nebulous that results in too many judgement calls. So not saying that the policy's perfect, but it's the best we've got right now, subject to new ideas that everyone will find agreeable. Putting a giant sign that says "by coming here, you agree that you could have shows ruined for you at any time" really isn't feasible, even if that wouldn't bother you (or possibly me) all that much. (And, as an aside, pretty much all the mods and admins have had to build up an "immunity" to spoilers as we review all the reported posts that contain the spoiler in plain text...
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