Why Is A Law Needed?

In Arizona, they have made a law against infringing on gun rights. My question is, why the hell do they need a LAW to stop states from infringing on constitutional rights? Doesn't the very fact that the Constitution PROHIBITS infringement on gun rights in America rule? Will a LAW be obeyed any more than a constitutional provision? If any LAW is needed here, it should be to PUNISH legislators who make laws that DO infringe upon constitutional protections. They should not need a LAW to keep people from violating the Constitution. The constitutional prohibition alone should do it. Seems to me they just want to complicate things by making more and more LAWS to do the same things already covered. (Bearing Arms)