> And yet it is currently a topic of debate.
Its constitutionality and meaning are not under debate. It is quite clear.
There's a debate about repealing it, which would require a new amendment.
But there's no serious debate about the existing amendment's interpretation.
The nuance that you run into is that legal opinion defining what 'subject to the jurisdiction of the US' means (from the 14th amendment) was made in 1898, but at that time the border was relatively open.
Immigration restrictions started amping up exponentially in the 20th century, especially amidst the world wars. It seems unlikely that the court would have ruled as it did in the context of these new laws.