I couldn't watch the whole video because it is too depressing. My first thought was how the policeman was obviously not trained to serve and protect, but rather to control and harass. However, my second thought was at least he just tasered the man, rather than killing him, as is often done to black and brown people.
I get that policemen have a risky job, but they should not EVER forget that the job of ANY public servant, which a policeman is, is to cause no harm. There was absolutely no reason or that officer to demand that citizen's ID or to taser him. The man had already told the officer that he did not have any ID on him. Police officers should be required to know the laws. If they don't, they and their departments should be held accountable for even the slightest abuse of power.
Despite the questionable legal status of Arizona's immigration laws, there is no place in the nation where simply being in public without ID is illegal.
However, there are several states in which it is an arrestable offense if you refuse to identify yourself to police. The U.S. Supreme Court has ruled that these kinds of laws can be legal, as long as the officers had reasonable suspicion to detain you in the first place.
In states with these laws, like Arizona and Nevada, you may be required to give police your full legal name. But you don't have to answer any other questions, and you shouldn't need any form of identification.