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)..
