Your argument against rudely asking for citations is perfectly reasonable. Personally, I don't find "[citation needed]" to be particularly rude, but of course tone is difficult to convey in text, especially with a neologism developed in written rather than spoken conversation. So, if you feel that the particular phrasing is rude, your opinion is as valid as mine. I don't know how it was intended when it was written, and neither do you really, so there's nothing more to be said about that.

However, what I have been arguing against are your arguments against providing citations, and your arguments against asking for citations, with both of which I take issue. Asking for citations rudely is wrong, but asking for citations in general is reasonable, and providing citations generally is a good idea.