Parent's argument is that the government already has photos of all international travelers and the government already has a written record of each international

Parent's argument is that the government already has photos of all international travelers and the government already has a written record of each international arrival and departure. So, the delta between a written record of border crossing and a photo record of border cross is the government having additional photos of somebody they already have at least one photo of. For many people, the difference between a single photo and many photos is minor. Government does not already have photos of all individuals who cross street corners (there is no legal requirement to have ID) and government does not record a list of names of each person who crosses the street. So, cameras at street corners have a much larger delta - between no photos and photos and between no internal location records and having internal location records.