I've actually wondered this myself, Bitter. The 'DO NOT' tag doesn't actually keep people from downloading and editing photos, it just prevents them from re-posting edits. I've downloaded photos numerous times on people who say do not, just to edit and see what I come up with. It's a shame in those instances I can't repost the edited image to help them understand what I might be talking about.
For me, it's far easier for me to understand someone's critique if they can show me.
Sorry, but to me that is ground for being dismissed from the board. I, however, don't make those decisions. It's bold faced disregard for the fact that someone has already made is clear they don't want to playing with their images. The tag doesn't say "My photo ARE NOT ok to edit, and then repost", it say they are not ok to edit, period. It doesn't matter if you never repost, you're going again the wish of a board user and the rules of the board. And, without the consent of the creator, which is what the ok to edit tag gives, you are essentially stealing someones images. Which while it's commonplace on the web, I would expect differently from a community of 'photographers'.