Is retagging other peoples questions such a sensitive matter than after a handfull of retagging opperations, the captcha challenge is thrown? Why?
In any case, I find it annoying; on the other hand I belive tagging done well really improve the quality of a question so retagging surely should be encouraged correct?
While it is a good thing, and should be encouraged, any non-limited function is bound to be abused by some silly sod and his little script too. To make abuse a little harder the CAPTCHA is tossed up occasionally.
I recently did some re-tagging myself and found that if you're really taking the time to read the question and making sure that you're not fixing one tagging error with another you won't hit too many CAPTCHAs.
The goal of the captcha is not to prevent you from improving the quality of tags (in fact that is greatly appreciated), but to ensure you're a human that's making the changes. If you or someone else with the necessary rep, decided they want to tag as many questions as possible with jeff-is-lame, you could, but fairly quickly you'd get shut down likely receive some punishment. What captcha prevents is it adds another barrier preventing you from writing a script that tags everything with jeff-is-lame. In the first scenario maybe you even affect 100 questions before getting stopped, in the latter it could 100,000.
