“The law is the law” means your argument has no way of winning because the law has already determined that your argument has no merit. No matter how outdated/outrageous/ridiculous/stupid a rule (or law) might be, too bad.. because it's the law. While littering is a problem, a bigger problem is when the ones enforcing the law apply it literally, as if their human judgement is not needed. If that is the case, we can use robots now. In this drawing, we can clearly see that the shipwrecked man is trying to throw a SOS bottle into the ocean. However now he must be punished by the law, because it doesn't matter if his act was a last attempt to save his own life, the law is clear against littering, and so the police man now makes sure it is being applied.