After reading all of this thread, I don't really know what to say first...
Well, first of all, most English Edited Manga groups do credit the mangaka, even if they don't put the name romanized, they keep it in Japanese (except for some cases where the name is out of the panels and is unwantedly covered by the rebordering). And we all know, and all leechers know (I hope so) that we don't make the manga. If they want to know who is the author or the publishing company or the magazine in which that manga is, they can find it easily searching the web.
Now, we English Manga Editors take our time to clean the raws and give them quality (lower or higher, but always better than the raw untouched, except for some speedy shitty scans), and some of us pay for the raws that we get. The least we can ask for is a credit. And that credit should be provided by following the rules we want, since after all, if you don't like our rules, just don't use our scans.
Now, for international Edited Mangas, people can't know who they took the manga from, without a credit page. If they use our scans, since we've cleaned them, they should aknowledge us, just like we aknowledge the mangakas. It's not such a bother to add a damn credit page, imho. If the group requests you to add a mention to them, if you don't have a credit page of your own, you can just add a mention in one of the pages, it's not that hard. And if they request you to add their credit page, is it really such a bother to take a file and add it to the release unchanged, when you've already taken all other files in the English release and modified them...?
About watermarks and forbidding: I'm completely against that. But have in mind that Manga Editors do that because they're sick of international releases using their cleaning without a single credit. If you were in the same situation, what would you do? And besides, if international Manga Editors credited the English groups in the first place, there would be no watermarks and no forbidding at all in any group. The problem about that starts only in the international Manga Editors who don't credit,
not in the "selfish"
English Manga Editors.
As an addition: I've been an international translator and Manga Editor myself, so I know by first-hand.
And I think that's all I wanted to say... Maybe I missed some points though.