Actually, the facts are on trial, the law is not. You are free to jury nullify, but no judge is going to allow an open discussion about the constitutionality of the law.
I know you don't like that, but it doesn't matter what you don't like.
No judge has the constitutional power to stop a defense opening/closing statement, or expert testimony about the constitutionality of the law as it applies to the case at hand. -- That is the issue.