In the military we were held accountable for any unlawful order we carried out. It was not considered a defense to claim that you were "just following orders". I don't see why a police officer being given an unconstitutional order should have any less burden than the military does in this regard. We have not seen it in this country in many years, but laws can and do get passed that are unjust, unethical and immoral. Just because it has an official seal on it does not mean you should blindly enforce it.