The authors of the Fourteenth Amendment guaranteed citizenship to all people "born or naturalized in the United States" for a reason. They wished to directly repudiate the Dred Scott decision, which said that citizenship could be granted or denied by political caprice.
They purposely chose an objective standard of citizenship -- birth -- that was not subject to politics. Reconstruction leaders established a firm, sound principle: To be an American citizen, you don't have to please a majority, you just have to be born here.
Then Reid said of Republicans pushing the issue, "They've either taken leave of their senses or their principles."