Against horrible software practices, the gods themselves contend in vain." — Friedrich Schiller (paraphrased)
A few problems with this. I write as one who doubles as a technical writer and who has spearheaded design docs at many companies. I will not take a client who wants me to work without a spec.
1) Most developers don't like writing documents; a lot of TDD fanatics say documentation is obsolete. But they're morons.
2) Even fewer can write clearly and thoroughly; I saw a guy paste a class definition into a document and there he was stuck. "The night was ..."
3) Even fewer will take the time to read them. A lot of developers are still kids, having grown up channel-surfing, gaming, and other low-attention-span activities and have never finished a book that didn't have lots of pictures. As a writer I have had to adapt with shorter paragraphs and lots of bullet points. They won't read the documents.
I'll write a doc even if nobody else is going to read it because it does me worlds of good in organizing my design.
One job I just finished thought their bug list was design document. I warned them. I was right. The project got hopelessly behind.