I feel there is a larger philosophical question here. If a law cannot be enforced, should it still be made into law, to signal the expected behavior to law abid

I feel there is a larger philosophical question here. If a law cannot be enforced, should it still be made into law, to signal the expected behavior to law abiding citizens, or should it be left out of the books? Say for example there is a untraceable doping substance that gives an unfair advantage. Should it be put on the banned substance list even if we can't ever prove usage?