First, I would never pass or vote for such a law. Second, if I were the police, I would not make an arrest. Third, if I were the prosecutor, I would not bring the case to trial. Lastly, if I were a juror, I would not convict.
But that's me, and I don't live in such a gun-free zone. The people who do are certainly entitled to enforce their laws.
Or are you saying that they cannot?