I like the granularity of removing the post rather than the poster. Most people who write an offensive/inappropriate post can and will write other posts that aren't.
I'm not a fan of the moderated-board concept as implemented on SI, but will also quickly acknowledge that while I was working there I didn't see it get completely as bad as I envisioned it could. Close, though.
At most, I could see board-specific exclusions being an Admin tool, though.
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