The laws on immigration have not been followed throughout the years. It is easy to be born somewhere else and seem like an American (looks, language, accent). The problem with the immigration issue causes the original people of a particular country to lose jobs, money, and rights. If we know exactly where the people in the country are from, there will be less problems with jobs and crime. Even if people are visiting from other countries, it would be safer for us to know where they are from.
Requiring citizens to carry a national identification card is a terrible idea. It is completely antithetical to a free society to be subject to the whims of some federal enforcement agency who could, at any time, ask to "see your papers" and subject citizens to stress and humiliation and worse for not having their card on them.