This reminds of me a documentary on a Mexican Prison I watched recently, the warden explained that on visiting day, they have very long lines of people waiting to visit inmates, he said they do try to ‘vet’ as many as they can, checking them, scanning for contraband, but admits it would be impossible to thoroughly search and check everyone coming in, due to the large amount of people and short window of time for visiting.
Same thing with taking in refugees, it would be literally impossible to vet each and every one and avoid a terrorist slipping in.
