I'll paraphrase my response from the other thread referenced
Creating a D&D game that was a RPG morality play would be more in line with an absolute alignment, the world in the Bible, and in morality plays, has an alignment that its players are rewarded and punished for acting in. To me though D&D works better as heroic or chivalric tragedies and romances, people should have absolute ideals which make them heroic, and fatal flaws that betray them. How I'd put that into alignment terms, you believe in something, but are not always able to act in those terms. Falling short of that alignment doesn't change your alignment but it should have negative ramifications for your character, eventually you might find you no longer believe in something, possibly because you've come to resent its strictures, at which point your alignment changes. That's not exactly easy to do in a video game, but I think a point system like the Pathfinder games do, isn't a good approximation, 'farming' 100 ravenous goblins to gain +100 points of 'good' shouldn't have an effect on a single much more heinous act that you chose to do for selfish reasons but only amounts to +50 evil points.
This goes out the window when you get extraplanar of course, because alignment is actually material there.
Your alignment should be fixed, your character rewarded or punished for acting in it, and a system of determining your motivations should then inform what your alignment is.
...[not knowing] is interesting too, if alignment still existed but wasn't player facing.
Keeping alignment but keeping it hidden from the player is the best in terms of roleplaying.
Don't have the world reward or punish actions, otherwise there's only really one alignment which players choose to work against, make everything have believable causes and effects and turn alignment into a way to interpret those events. Unless the story involves extraplanar entities, Deities and the like.
