Nobody has said yet what exactly is wrong with redundancy. It seems useful to me. Sometimes its inflectional concord between words (which is a requirement of some languages and its absence would signal a grammatical error); sometimes it's for rhetorical effect (and we're all for that where and when appropriate); sometimes it's to avoid ambiguity (which seems a good thing, too); and sometimes it's something which annoys a select group of speakers (who usually seem wrong about other aspects of language, so I'd say it's something to do with them and not the language)..

Ceci n'est pas un seing.