I agree that a username should be removable. I have been thinking of it for the future myself. When my time on WP is over, and I'm not sure when that will be, I would like the option of removing the username for a variety of reasons:
* Its concise - like closing a book by putting it back on the shelf
* it prevents the accumulation of usernames that are unavailable to others
* your not taking up space on the site
* the name no longer represents you - or another person has problems with it, or bad associations come to it perhaps unknown at the time of making the name
* in your case, it protects your given name
* There may be cases where people open usernames in other peoples names as well, and those should be closed if the person wants it
etc...
obviously threads and such cannot be deleted, but it could be like Ebay. When a username is closed or changed it says (no longer a registered user) beside the name in question.