The issue is a "knowledge" problem. If a person wants to dive but has no certification, how do I know if it is safe for them to get in the water and dive. The mere fact of a certification does not solve the problem. It simply reduces the universe of unknown quantities. If I do not dive with divers without certifications I will never have to explain why I was diving with a diver without a certification. That solves my legal, ethical and personal issues about that subject.