Why doesn't the federal government want to pass Arizona's immigration law?

The main idea of Arizona immigration law is to strengthen immigration management and control immigration, which is contrary to the federal government's policy of supporting immigration, and the federal government naturally does not want to pass it. It is easy to understand that immigration will not only occupy local resources, but also bring potential problems such as crime and disease, which will do more harm than good. Local governments naturally don't want others to immigrate. But for the whole United States, immigration brings labor, talent and money, so the federal government supports immigration. So the contradiction came, so it was torn.