The Islamists aren’t going to have fewer babies, the illegals aren’t going to have fewer babies, the welfare moms won’t have fewer babies. The main groups this targets are middle-class and those who need to have more babies to keep Western Civilization alive.
From what I read, as soon as Islamists move to the West, their birth rates plummet. And they're not that high in parts of Islam-world, either. I thought that was interesting.