Yosharian
Arcane
Alignment is a useful tool to ensure consistency in player actions (while keeping in mind that intent is important).Codex will be unable to name a single thing that alignments actually contributed other than endless arguments on the internet about what is right and wrong, what is lawful, what is good and so on, and so forth.
If my Paladin decides to start going around animating corpses and using them to fight for him, I can explain to him that that act is considered evil in my setting and thus he shouldn't do it if he wants to keep his powers (which are granted to him by a Lawful Good god). Of course if he wants to go rogue, that's fine - it's his choice.
There is some merit in arguing for alignments to be flexible - they can be too strict sometimes, and using them as a tool to force players to act how you want them to act isn't good for the game.
But acting like alignment is utterly useless and it's never had a purpose in the game is ridiculous.