He did NOT call our Immigration laws immoral. What he actually said was allowing our current system of turning a blind eye to the illegals so they can be exploited for cheap labor is immoral.
“Is it moral for us, for example, to take advantage of cheap labor from illegal immigrants while denying them citizenship? I'm sure you can tell from the way I phrased the question that I believe we have taken the moral low road on this issue,” he wrote.
http://www.ontheissues.org/2016/Ben_Carson_Immigration.htm
Carson has also said the United States should model its immigration reform after Canada's guest-worker program. “People already here illegally could apply for guest-worker status from outside of the country,” Carson wrote in November. “This means they would have to leave first.”
Yes, Carson believes it is immoral to deny them citizenship.