I think someone was trying to make a distinction between vast majority and small minority. Yes, some firearms are used to commit crimes but only an extremely small minority of firearms in the US are used for such purposes (as in 99.999% are not used for criminal purposes). So yes, some sites are used more heavily for non-infringing purposes and some sites are used almost exclusively for infringing purposes.
Overall, I agree that shutting down types of sites is wrong. However, shutting down individual sites based on their usage and how they promote themselves, etc. may not be. To continue the gun analogy... shutting down licensed dealers and gun shows is generally wrong but shutting down the guy selling out of the back of his van in a back alley in downtown big city is probably a good way to prevent guns from being used for criminal activities.