It always takes time to fully grasp the content of Clay Shirky articles, especially when they try to summarize a complex debate as ontologies vs. folksonomies. In his response to Gene Smith, Clay shows no doubts:

Tags are a useful, even vital, tool for anything that can be referred to with a URI. Which is a pretty considerable subset of everything.

He is also quite certain about the final result of this match:

People who believe that tagging will co-exist peacefully with classification schemes have underestimated tagging.

And the reason to make such a strong statement is not ideological but economic.

Categorization systems favor stable categories not because the world is stable but because categorizers are busy and their time is expensive.

For all the many differences between tagging and classification, the key one is cost. It is simply too expensive to hire professionals to do the work once a system that uses peer production is also available.

I think this is true and applies both to professional and amateurs categorizers. Rearrange an ontology in order to be coherent with the reality it tries to describe is a a big hassle not just for the librarians of big institutions but also and especially for amateurs involved in organize their weblog posts or their pictures. Unless they use a tag enabled blogging software or Flickr!

In the final part of the post Clay is even a bit cruel with Gene, easily dismantling all of his three examples (Amazon, Wikipedia, Yahoo) aimed to demonstrate how classification is sometimes the only right answer.