In my opinion, if they came here legally on a tourist or immigration visa then they have consented to be subject to the jurisdiction of our laws and yes, if they were to have a baby they would be BOTH born on our soil AND subject to our jurisdiction.
On the other hand, the child of an illegal who chose to live outside the jurisdiction of our laws only meets ONE of the TWO requirements.
I think there is lots of room for argument on these points. The other side can also make some very valid points. The Constitution puts sole authority for determining our immigration policies in the hands of Congress. They, rather than the courts, should decide what the clause means.
I agree with the points you are making. I guess we should ask WWFD. Would they want Congress to make a law or amend the Constitution. I still think that an amendment is required.