What is the purpose of having a Visa in place?

The immigration background was a very different experience that what I had imagined.  The whole idea started with Aristotle when he proposed the idea of having people actually be part of a state, rather than just living in it. Aristotle said that just because people live in the same area, the people are not one with the state.  He went on and said that the people are citizens when they have some influence in how the country should be ruled.  He continued to talk about a democracy, where the people control how the government should act and all peoples' powers are equal to one another unless elected to have more power than the people.  Abraham Lincoln talked about a government made by the people, for the people during his great speech at Gettysburg.  Some countries believed that if a person gets in trouble with the state, then that person should lose his or her citizenship because the lack of control to be part of the country.  Immigration is one of four ways to become part of the state, the other three are to be born in the state, marry a citizen of the state, or naturalization which comes over time.  Between the 1990 and 2000, an estimated 9 million immigrants came into the country with visas supported by their friends, family, or people who want to help immigrants move into a "better" life, future, and or opportunity; the high amount of immigrants that cant get visas and enter into the country illegally, the job opportunities are getting smaller and smaller and the consumption of goods is getting less and less.  This caused the economy to drop.  People who came in to the states with visas, pay money to the US treasury which would help financially support the country as a whole.  This also amounts to people getting pay, thus the US would end up losing their money.  Asian students who came into the US for the purpose to study, with the study visa, contribute about $12 billion into the US which show how many people actually apply to get a visa and how much they contribute to help out the US indirectly.