I don't buy the "ends justify the means"-type arguments. I don't believe that private corporations setting themselves up as law enforcers through surveillance of their customers is a worthy or desirable situation. By the same reasoning, one could argue that ExxonMobil should be allowed to set up roadblocks and checkpoints to check for drunk drivers because "stopping drunk driving is a worthwhile goal", or maybe Coca Cola could bring a team of drug dogs to your office to make sure there isn't any illegal drug activity because "illicit drugs are bad". The problem is not in the stated goal (i.e. help curtail child porn), the problem is in a private corporation getting into law enforcement. Since they are not government, they are not subject to the Constitution, hence all of our normal protections against unlawful search and seizure are moot. If we allow corporations to become a shadow police state, we've got much larger problems than child porn.