That ruling was simply wrong. Today's court will likely rule correctly. The purpose of amending the constitution was to etch the 1866 Civil Rights Act into stone, making it almost impossible to deny blacks citizenship. There was a debate on the topic. The new language was a heated debat, and the text is still debated over today. But passage would not have occurred without the voting congress believing it would not be used as broadly as it is now.
The Citizenship Clause was proposed by Senator Jacob M. Howard of Michigan on May 30, 1866, as an amendment to the joint resolution from the House of Representatives which had framed the initial draft of the proposed Fourteenth Amendment. The heated debate on the proposed new language in the Senate focused on whether Howard's proposed language would apply more broadly than the wording of the 1866 Civil Rights Act.
Howard said that the clause "is simply declaratory of what I regard as the law of the land already, that every person born within the limits of the United States, and subject to their jurisdiction, is by virtue of natural law and national law a citizen of the United States." He added that citizenship "will not, of course, include persons born in the United States who are foreigners, aliens, who belong to the families of ambassadors or foreign ministers accredited to the Government of the United States, but will include every other class of persons" a comment which would later raise questions as to whether Congress had originally intended that U.S.-born children of foreign parents were to be included as citizens.
The 1866 civil Rights act did not allow anyone born here automatic citizenship. Again, the purpose was to give former slaves citizenship.
en.wikipedia.org