I believe Mel does represent the Spanish as being good as he shows a cross being held by a priest in one of the boats as it arrives. Given Mel's Catholicism, the cross symbolizes being saved, which is what happens to Jaguar Paw when the Spanish arrive with their cross.
Also, the movie does destroy the "Noble Savage" myth. The Mayans were "uncorrupted" by Western Civilization or Christianity, from the liberal point of view, yet they engaged in horrendous and evil acts. The Spanish Catholics stopped the human sacrifices and cannibalism. Western Civilization is a clear improvement on what the average Mayan was enduring at the hands of the witch doctors and other Mayans.
I do think your interpretation of the Durant quote is correct. Mel believes that the West may be in danger of repeating the mistakes of the Mayans.
This interpretation is however only possible if one has foreknowledge of Gibson's Catholicism. To view the movie as self-repesentational, I think one should subtract that. (I state this with all due respect to and in full recognition of what the cross symbolizes in Catholicism, Catholicism, and Gibson's Catholicism.)
Also, the movie does destroy the "Noble Savage" myth. The Mayans were "uncorrupted" by Western Civilization or Christianity, from the liberal point of view, yet they engaged in horrendous and evil acts.
No, the noble savage motif (in my opinion) only applies to the jungle tribal Mayans, not the "civilized" Mayans. The jungle tribe did not practice those evils. (NB: by this time in history, I believe historians generally concur that Mayan civilization was in decline and Mayans no longer had a central uniting government or ruler. They had reverted back to city states or back to subsistence lifestyles in the jungle, depnding on the time and specific location.)
Western Civilization is a clear improvement on what the average Mayan was enduring at the hands of the witch doctors and other Mayans.
Mmm, well, just to take the devil's advocate view (apologies for the pun), the peaceful co-existence of the jungle tribe with their native ecology is shattered by the civilized but evil, industrialized Mayans. Without overly spoiling the plot for any future viewer-readers, the movie does depict that the peaceful, environmentally friendly jungle Mayans had a chance to embrace Catholicism and Western civilization, but in the end, they declined. So the ideal of the Noble Savage is upheld, at the expense of both Mayan and Western civilizations. The notion that "Western Civilization is a clear improvement on what the average Mayan was enduring at the hands of the witch doctors and other Mayans" is IMHO-- as much as one might be inclined to cheer it and/or Gibson-- a projection onto the movie rather than the main message that the movie itself contains.