Eisenreich is the worst of the list if you ask me, but every year there are a few guys on the list that obviously don't belong.
I remember seeing Roger Maris' name on that list for years, and his career numbers are worse then Fielder's, except that he did break the HR record. A marginal player usually needs a "special" season like that to get on the ballot, and Fielder's 51 HR in 1990 probably did it for him. At that time he was only the 11th player to ever hit more then 50 in a season, and only the 3rd since the record fell back in 61'.
Of course, 50 HR has no magical significance anymore, especially since Brady Anderson did it in 1996, following it with back-to-back 18 HR seasons. And steroids or fish tranquilizers or whatever these guys are on has no effect on our game at all. (that was sarcasm by the way).