tl;dr:“Is it ever a good idea to use natural keys in a database design? My experience tells me that it's not. Ultimately, regardless of how certain you can be that the natural key is stable and correctly tracks the entity that it's supposed to keep track of, data errors will occur. This includes errors in those natural keys.”
tl;dr:"We need young people in the software development industry. Because of their vigour and inexperience, they'll push the envelope... We need old people because they're in a position to speak truth to the world." Mark points to the fact that older people have less to lose and "many are in the unique position to reveal truths no-one else dare speak."