He had NO AUTHORITY to make such a determination. He was charged with making a determination as to whether the policy on its face was a violation of the establishment clause. He was not charged with resolving the scientific dispute over the validity of one theory over another nor did he have jurisdiction to make that inquiry.
But the Lemon Test goes beyond the mere letter of the law and forces the inquiry into the motives of those who made the policy. That is a dangerous thing to do. If this policy had been instituted by concerned atheists or concerned Bhuddists rather than by concerned fundamentalists, then the policy would not even have been challenged.
Think about that, please.
Why not? Along with all of the other aspects of the case we've examined on this thread, he looked at the evidence at hand, and it was clear which side was telling the truth, and which side wasn't. Big hint: If you have to lie to get your views put in a public school science classroom, then those views don't belong there. Moreso, if you have to lie to get schoolboards to put your views in a science classroom, then they definitely don't belong there.
This case was decided correctly on multiple levels, any one of which would have been correct in its own right, but placed together are simply devastating! At the very least, the defendants tried to place a non-scientific idea in a science classroom, they tried to establish a Christian idea in a classroom to the exception of all other religions, and they quite possibly perjured themselves in doing so(certainly they lied to their constituents).
Certainly, if someone can untangle an actual theory of ID that's independent of religion there is a chance to get ID in a science class, but with the current incarnation that is extremely unlikely for a while.
I disagree with you on your last statement, completely and utterly, I think if some other religion tried to pull this stunt, the Christians would be on them in a flash--and they'd be in the right.