It's necessary to read the entire summary to grasp the very narrow legal issue before the SC. This stands out:
"If the justices were to agree with the Trump administration, the Maryland challengers posit, 'chaos would ensue,' because birth certificates the documents normally used to establish U.S. citizenship will not be enough even for children born in the U.S. whose parents are U.S. citizens. Instead, they suggest, state and local governments will have to develop new systems to verify citizenship, at significant expense, 'and anxious parents-to-be will be caught in the middle.'"
"On the issue of birthright citizenship, they emphasize that the text of the 14th Amendment 'guarantees citizenship to all born in the United States and subject to the jurisdiction thereof' which the Supreme Courts cases and the federal government have long recognized to include virtually all children born in the United States, regardless of (among other things) the immigration status of their parents."
"And although the federal government attempts to narrow the scope of the phrase 'subject to the jurisdiction,' the Washington challengers tell the justices, 'the group of U.S.-born individuals not subject to the jurisdiction of the United States is both extraordinarily small and well defined.' For example, they write, it includes the children of foreign diplomats who are born in the United States, as well as those of foreign troops who are in the United States because they are at war with this country."