Real Person Fiction is a time honoured tradition which was already practised by the Judean Nevi’im (a word which was somewhat mistranslated as "prophets") who spoke prophecies of their past and contemporary fellow men (both positively but often negatively), and by the ancient Greek scholars (e.g.: Plato's dialogues with his mentor Socrates are clearly RPF). It continued to be practised throughout history, with relatively few moral obstacles until in the 20th century, fan fiction and RPF started being held in contempt due to copyright maximalism.
I now realise that fan fiction and especially real person fiction can also be used to help combat the flood of new characters and names that plagues many more "original" stories. People generally have a rough concept of what characters such as Chuck Norris, Emma Watson, Richard Stallman Moses, or Miss Piggy, are like and generally can better remember them because they thought about them a lot.
The reason some people criticise RPF writers of being villains is due to the fact famous actors have been facing increasingly harsh treatment due to the professional (= working for money), non "open", and "original" nature of Hollywood that has been declining in effectiveness following the open source and open content trends. (Whether they are fully "free/open" or only partly so - see Richard Stallman’s opinion about the Creative Commons licences.)