The historical perspective:
For many years in Greek times, citizenship was an issue. Typically, citizenship was granted only to those who were descended patrilineally from those who were present in the city at a certain period when citizenship was defined. When cities like Athens grew larger, those whose families had immigrated long ago were still not given citizenship. Instead, they formed a class called the metics. Metics could not earn citizenship, regardless of how long their family had been in a polis. However, like our resident aliens now, they had to pay taxes and serve in the military, but did not have the rights of citizens, including voting, owning property, and setting up shop in the marketplace without paying a tax. This system ultimately caused the Athenian form of citizenship to fail to the greater Roman form of citizenship, which was more freely granted to aliens and conquered peoples. Later, English Common Law established jus soli, and brought about a new, more superior form of citizenship that has worked for hundreds of years in many countries.
What the US would be like if there were no birthright citizenship:
Imagine a United States without birthright citizenship. Surely, some resident aliens would be able to go through with the process of becoming a citizen, but it would be very slow. If such a policy had existed from the nation’s founding, almost no Massachusetts residents (largely descended from Irish and Italian immigrants of the late 1800s and early 1900s) would be citizens. Asians would have no rights. Almost anyone who wasn’t English from colonial times wouldn’t be a citizen. Immigrants made our nation, and without birthright citizenship, America would be a much different place.
The race argument:
While this is the weakest argument against repeal, it is still significant. The citizenship clause was designed to protect the rights of African Americans after the Civil War. It was the clause that ended the Black Codes. Without the clause, there is no Constitutional protection to prevent laws like the Black Codes from being passed again