>>644
Lots of people have pointed out that the alignment system is dumb, that L/C and G/E aren't treated as properly orthogonal by the rules, blah blah blah. I'd like to propose something different.
Back before the ‘A’, D&D had just Lawful/Neutral/Chaotic. This was taken directly from Weird Tales-esque fiction, significantly Moorcock. The alignments were directly embedded into the settings of those stories, though: there were tangible (well, sometimes) forces of Law and Chaos at work, and heroes were often servants of one of the other, willingly or not. Good and Evil were complex shades of relativism and perspective, Law and Chaos weren't. This worked, because lots of DMs wanted to run those sorts of settings and the liked those rules.
Sometime before the ‘A’, a Good-Evil axis was added. I've never seen an authoritative reason for why, but my private suspicions are that the games at the time, which were huge, multi-group affairs, wanted to use alignment as a way of distinguishing individual factions of players, and L/N/C wasn't enough. This way, G/N/E would represent a character's individual motivation, and L/N/C would represent how that character was being used by destiny (partially affected, of course, by the character's own desires).
Most games these days don't use Moorcockian settings, and instead leave alignment to be a rough approximation of personality. This leads to bizarre arguments over whether Robin Hood was Lawful (for sticking to a personal code) or Chaotic (for choosing a code that differs from the local legal authority's), and to whether one's alignment changes when crossing international borders.
The upshot, I think, is that paladins' alignment restrictions make perfect sense, but only if you have a setting in which alignment directly means “serves THIS higher power, intentionally or not”, and in which those higher powers happen to be labelled LG. In that situation, for example, falling makes perfect sense: it's not so much that the paladin is being punished for not toeing the line as that, through whatever circumstances (intentional or not), the character's destiny is no longer moving in the direction LG wants it to go, and it makes sense for LG to cut losses. (Of course, that's still not a very fun mechanic for the way today's games are played, where players are supposed to have personal connections to every character they play and write up a backstory and blah blah blah.)
A Batman-like paladin, in such a Moorcockian setting, would be a perfect candidate for a semi-willing servant of a paladin-sponsoring entity. But, since alignments operated in scales of conflicts far beyond human understanding, you could easily have situations in which Law says “Actually, as part of our final endgame, Robin needs to die right here, so your healing powers are temporarily revoked. Good job punching those demons, though!”.
(Of course, the best thing would be for DMs to alter the rules they use in order to thematically support the setting they want to run. Alignments would usually be the first thing to go.)