There seems to hardly be any way to have your cake and to eat it too - I mean retaining some of the benefits of the credibility carried over from the old name to the new name, so of course, there can be some benefits in changing your user name, but seemingly the ONLY way to completely lose the connection of the possible negatives that have come to your old user name would be to create a new account and to really start over.. and maybe not even mention the old user name in connection with the new account.
There is also security through obscurity, too.. and there are likely other means of attempting to NOT draw the wrong kinds of attention to yourself.. and the interwebs are filled with fucktwats..
This would be something theymos could create: a new rank that shows you're an old user, without disclosing your old account.
If Admin only creates such accounts for users who made a name for themselves, it could be a solution to have and eat the cake!
I too wouldn't mind having more privacy, but once it's gone, there's no way to get it back.