Vetting of people coming in legally is a totally different situation. If someone makes a specific decision to apply for a visa before moving to a country they have plenty of chance to prove who they are with documentation, the documentation can be checked and specific requirements can be laid out. Asking for documentation from someone who fled their home via the back door as the local warlord's henchmen kicked down the front door is unlikely to be fruitful - it's probably safe to say they didn't have chance to gather up their birth certificate, marriage certificate, education certificates, professional qualifications, police records and the like.