In the late 1660s the Iroquois village of Oneida--still pagan at the time--had become an absolute mess. Drunkenness, violence. Torture of captives not unlike the scene narrated above. Even measured by pagan morals, they clearly had fallen from the noble example of their ancestors.
A few Oneidas converted and founded a new Iroquois village near Montreal. They basically kept their Iroquoian culture, but they also made a rule that to live it this village, you had to give up your vices and live Christian morality....and they actually expelled other Indians for not upholding it.
Long story short, this village attracted so many Iroquois over the next few years that the original Iroquois villages got jealous and complained they would be entirely depopulated.
Christianity helped save Iroquoian culture. From itself.
The book of Judges is an historical account of the following cycle: Israel is in bondage and cries out to God. God sends a Judge to deliver them by way of His power. Israel prospers and turns away from God. God turns them over to themselves. They deliver themselves back into bondage. There are variations, but the cycle is clear and instructive.
The only difference is that the Iroquois had always been turned over to themselves. God delivered them from their self imposed bondage.
I have a concern regarding your statement, "they clearly had fallen from the noble example of their ancestors." It directly implies that there was a prior time when Iroquois behavior was noble. I don't know, but I sincerely doubt it. The general history of native Americans tribes is that they treated each other with utter cruelty and barbarism. It is complete fiction to believe North America was some sort of Shangri-La before outside influence. It was Lord of the Flies on a continental level.
Regardless, the facts we know indicate that Robowombat's statement is well rooted in revisionist history. Dances with Wolves is fun to watch, but it is fiction.