I don’t like the former, but don’t see an issue with the latter. Having your name associated with a flag could discourage people from flagging actual violations, and could create a culture of vengeance flagging. In addition, trolls who thrive on divisiveness and conflict could easily create accounts using the names of posters against which they have a vendetta to make it look like those posters are abusing the flagging system.
Sure, it is possible to confirm the actual bnet tags to see that is going on, but it adds a layer of uncertainty and another avenue for harassment. I do believe that anonymous reporting has flaws, both on the forum and in game, but fewer flaws than some alternatives.