It's really important that we (the people who believe in prototyping and iterative development) emphasize that this is not a chaotic way to approach a problem. We absolutely do plan - however, we plan by coding and prototyping, rather than writing detailed specs. Specs are good - but they emerge from the code and the prototype. We absolutely do consider design issues - however, we discover and implement these things through refactoring. And in the end, we may very well throw out our first approach and rewrite, if it appears to be necessary.

But I think this is leaving the realm of opinion and entering the realm of reality. The people who try to do the pure waterfall where an architect designs and writes specs, a coder writes code, a tester does testing - they seem to be losing badly in the race to get excellent software to market. From what I've read (successful startups, Google) the free market appears to be rewarding the better approach.