Panda and Penguin in Google SERPS introduce negative factors to the overall calculation of relevance.
Instead of returning sites with the highest positive relevance scores (by whatever criteria these are measured) in top positions, things that previously simply didn't count towards a positive score are now given a negative value.
Also, instead of adding to a positive score on an ad hoc basis (i.e. whenever new elements entered the index), Panda and Penguin actively seek out factors that add to the negative score. That, in my view, has all the hallmarks of a Witch Hunt. I don't know of a Witch Hunt that has ended well.
Saying that a negative factor isn't a penalty is denial by semantic inexactitude.