An estimate is 40,000 such anchor babies per year.
So about 1% of total. Doesn't sound like a problem that's worth messing with the constitution and making 4 million US families each year go through federal bureaucracy. And look on the bright side: 40,000 non-abortions. That's gotta outweigh the disadvantages.....
That's not the perspective of people that live in a county that's overwhelmed with the problem.
But yours is a common attitude, for people far removed from the everyday implications of it.