Fischer consistently played 3.Nc3 because he believed the Winawer is antipositional; Black puts his central pawns on white squares and then trades off his black-squared bishop. The poisoned pawn variation attempts to take advantage of that quickly. Smyslov used it fairly often, particularly in his world championship games against Botvinnik. I suggest you study those games.
That's very interesting, and I agree with the antipositional nature of the Winawer. I personally love to play the poisoned pawn variation as White, but Black normally chooses to castle instead, and a blocked game ensues.
I don't think you can use Fischer as a basis of whether any opening is good or bad since he pretty much beat everyone.