I firmly believe that the myriad of real world personalities and nuances cannot be reflected by D&D's rather comic-book like Alignment system.
You can make basic assumptions like Hitler was Evil and Mother Theresa was Good, but beyond such polar extremes, Alignment cannot easily capture a real person's true personality.
For myself, I can be extreme ordered and law abiding one day (i.e. Lawful), and very anarchic and anti-establishment (i.e. Chaotic) the next, depending on circumstances, my mood etc.
Someone who is a devoted family man and pillar of the community (i.e. Good) can snap one day and murder his family (i.e. Evil).
Alignment arguably works as a game concept, but I really don't think it can refelct the real world.