Folks reading this shouldn't be down on Cruz without at least watching the brief video at the source in which Cruz clearly explains himself. He's certainly not in favor of birthright citizenship, but he's in favor of the Constitution and he doesn't think birthright citizenship can be overturned absent a constitutional amendment. Rather than spend present efforts on the difficult amendment process he'd rather close the border: if the illegals can't get in they can't produce anchor babies!
Whether birthright citizenship could be overturned by a simple act of Congress is presently best described as a controversial legal position. There are respected legal minds on both sides. Personally I think its possible, but Ted tactically doesn't want pursuit of that to detract from getting the wall done.
As long as he's agreed that the 14th amendment needs clarification to prevent its further abuse.
There are plenty who arrange travel plans to be here - legally - when they deliver their babies, Its called birth tourism and a wall won't stop it.