As far as these arguments are concerned, as you can see, I think the argument "because tradition" has more than enough to settle the matter. Nonetheless, it deserves attention to go into arguments besides tradition.
Tradition is never a reason. Tradition is an excuse. There is no logic in an appeal to tradition, only a statement that the tradition is the speaker's emotional comfort zone and the speaker therefore prefers not to leave it. That is not rational, nor is it an argument- only an appeal to emotion. It is invalid to those whose emotional comfort zones do not include whatever the tradition is about.
But if tradition is what appeals to the reader, then consider this: Rule Zero is also a tradition in place from the earliest days of the game, and Rule Zero says the GM can break the rules when it suits him or her. Therefore, appeals to tradition on keeping rules like the LG Paladin are invalid on the face of it, because a different tradition says the GM is allowed to do Whatever. If the GM wants non-LG Paladins, the GM gets non-LG Paladins. QED.
(I don't have much to contribute to the thread besides the notation about my own world in the post way above, but "arguments" based on tradition have always gotten my goat in a huge way and I generally despise the people who make such arguments in real life.)