There's injustice everyday: O.J. Simpson killed two people, and Jonathan Vilma led a ring of New Orleans Saints players, who, aided by their coordinator and ignored by their head coach and GM, created a cash payout system for teammates who caused game ending injuries or worse. The NFL did a terrible job of proving this beyond a reasonable doubt, but that's of little matter to anyone outside of the Saints or their fans.
There shouldn't be sour grapes for opposing fans, mainly because of the four players in question, the two active Saints - Jonathan Vilma and defensive end Will Smith - aren't the kind of game changing talents that move the fictional win/loss needle. Since they won the Super Bowl, New Orleans' defense has found a way to absolutely collapse in key situations (namely the second half of their last two playoff losses). New coordinator Steve Spagnuolo is certainly a move in the right direction, but the return of Smith and Vilma won't magically make that team a Super Bowl winner.
The other reason to let this go? Player suspensions merited by evidence as shoddy as what the league produced is a scary precedent to set. I'm as sure of their guilt as I am of Simpsons, but in both instances those charged with proving it came up woefully short. Nobody died in this instance, and even the angriest anti-Saints fan still has the year-long ban of Sean Payton to hang their hat on.