I used to be in this camp but I've since changed my stance. I like having Peterson back there because of his sure hands and the fact that he almost never makes any negative plays (except when his protector decides to give him a shoulder shiver)
He is back there to first and foremost handle the kick, make one read and if he has a seam hit it, if not he just runs out of bounds. The key behind it though is that the offense is so good all we need out of the return game is to not mess anything up or make anything worse. I seriously think that is the philopshy. Just guarantee the offense the ball and we are good.
Also, if PR duty helps keep PP more engaged and has anything to do with how he is playing on defense then let him do it. Plus you never know, they might be in a situation down the road where they need a big return at the end of a game. There is no one on the roster that gives them a better chance for that. You don't want to all of sudden throw him back there when he hasn't been fielding kicks all game or possibly for weeks. Just something to think about.