That's a silly analogy. Everyone who gets on an airplane goes through a screening process -- that's 100% screening. If you search 5000 mass transit riders a day, that's only .14% of all passengers, which means there is a 99.86% chance that a person will enter the system without screening.
not everyone goes through the same screening at the sirport either. so what you are saying is that we should stop the "pull aside" checks at the airport then, since just a few people go through it. its either everyone, or no one.