1. The Constitution nor the 14th amendment confers citizenship to children born on US soil of parents who are subjects of another sovereign nation.
a) The language was clear and debated as such to be about "under full jurisdiction of the US, meaning, not still subjects of another nation".
b) When enacted, there was no issue and hence no discussion of people entering the US illegally and having children - that wasn't even on the radar; but the Native American tribes and former slaves and people in the country from other nations as visitors, ambassadors, etc. were very much discussed and it was clearly agreed that citizenship would not be conferred unless the parents were under full jurisdiction of the US.
2. The Supreme Court hasn't "ruled" on this, but shouldn't have the authority regardless, but in our day and age of giving authority to the feds for everything, hopefully will at some point. The "EO threat" was intended to do just that - to execute an order to agencies which would then be challenged in court.
a) The entire concept of "birthright Citizenship" is a relatively new concept and by no means became reality because of Constitutional powers. Like most other powers currently exercised by our grand federal government, it was simply "made so" by policy and never challenged as constitutional.
b) The existence of this "policy" in no way, shape or form, represents evidence nor proof that it is "in the constitution".
3. The argument that "all other nations" confer citizenship to children born to tourists or non-citizens is hogwash. No country in the EU does and only Canada among major, advanced countries does so.
FRANCE
Children born in France (including overseas territories) to at least one parent who is also born in France automatically acquire French citizenship at birth (double jus soli). A child born in France to foreign parents may acquire French citizenship: ... at age 18, if born in France on or after January 1, 1994
British Nationality Law
British Citizenship can be acquired in the following ways:
lex soli: By birth in the UK or a qualified British Overseas Territory to a parent who is a British citizen at the time of the birth, or to a parent who is settled in the UK or that Overseas Territory
lex sanguinis: By birth abroad, which constitutes "by descent" if one of the parents is a British citizen otherwise than by descent (for example by birth, adoption, registration or naturalisation in the UK). British citizenship by descent is only transferable to one generation down from the parent who is a British citizen otherwise than by descent, if the child is born abroad.
By naturalisation
By registration
By adoption
For nationality purposes, the Channel Islands and Isle of Man are generally treated as if they were part of the UK.[3]
Information about British citizenship and other kinds of British nationality is available from Her Majesty's Government.[4] Information is also available on provisions for reducing statelessness.[5]
Persons acquiring citizenship by method (2) are called British citizens by descent; those acquiring citizenship by methods (1), (3) or (5) are called British citizens otherwise than by descent. British citizens by registration, method (4), may be either, depending on the circumstances. Only citizens otherwise than by descent can pass on their citizenship to their children born outside the UK or a British Overseas Territory automatically; British citizens by descent can pass on citizenship to their non-UK born children only by meeting certain UK residence requirements and registering them before the age of 18.
Germany (BlueSky was stupid enough to think this equates to 2 illegals having a kid)
Children born on or after 1 January 2000 to non-German parents acquire German citizenship at birth if at least one parent: has a permanent residence permit and. has been residing in Germany for at least eight years.
More reading for those interested in having facts instead of emotion:
https://www.loc.gov/law/help/citizenship-birth-country/index.php