Then we shouldn't have let his parents in.
If we adopted an immigration policy in which no one from Algeria, or no one who is a Muslim, was let in, then we could have kept his parents out. But a policy tailored to keep out persons who may one day have a son who moves to Spain and becomes an al Qaeda financial supporter would not be very effective.
We should definitely be more careful in who we let in, but it is even more important that we eliminate birthright citizenship for children of persons who are not U.S. citizens or Permanent Residents, whether through legislation approved pursuant to Section 5 of the 14th Amendment or, if the courts strike that down, through a constitutional amendment.