I agree completely! I suspect the solution to the CAPTCHA paradox will be something we haven't even considered. In fact, I don't think we can even solve it directly- we have to approach the problem from a different angle. For example, we can start requiring significant identity authorization on some high quality sites (sacrificing anonymity for responsibility), and rely on advanced filtering for the rest.

Think about it: the actual problem with spammers defeating CAPTCHAs is low quality content. I'd much prefer to expend energy trying to stop low quality content, which is often delivered by non-spammers :)

I wrote a blog post expanding on these ideas: http://cmurphycode.posterous.com/the-problem-with-captcha