It is truly stunning the lengths you will go to try and make sense out of your position.
Hunter-gatherers and mennonites were extremely homogenous societies. They shared a set of ethos that were rigorously passed down by oral tradition. Social conformity was very much expected - you didn't have Femen living peacefully beside heavily religious folk. To even attempt to use them as a basis for governing our society, which has a simply staggering amount of internal differences, is incredibly irrational. The Iroquois, for instance, captured children of their enemies and then assimilated them totally into their culture, destroying God knows how many distinct cultures in the process. And yet this is something we are supposed to emulate?
The stakes are also much higher. Humanity cannot afford to "reach a consensus." We will have nine billion people to feed by 2050, so we can't exactly just wait for everyone to come around before making important decisions. For instance, the global warming debate still rages, and there will never be a consensus on how best to handle it - but in order to prevent mass extinction, we need to take action now, and use all sorts of coercion to reverse the ecological damage we've done.
It is sheer idiocy to suggest that the real important questions of our time could possibly be solved by consensus, especially considering all your examples are of groups that have already been annihilated, or are slowly withering away. I mean, do you realize how utterly damaging the consensus model was to the Iroquois? How badly it hurt their chances of survival? It totally handicapped them in the American Revolutionary War, and consequently, the Confederacy was more or less destroyed.
As is obvious to the rest of us, consensus is a worthy goal - but it is sometimes simply impossible to achieve, particularly when you are talking about 300,000,000 culturally different people and not 12,000 fully assimilated Iroquois. The complexity of our society is so much greater than that of indigenous people four hundred years ago that it defies all logic to even suggest that what worked for them (or to be more historically accurate, what didn't work for them) will work for us.
You really need to look up the Great Binding Law before you spout off anymore BS about lack of coercion. Over 110 clauses, with banishment from the tribe being common place for those who disobeyed.
From "Great Law of Peace," Wikipedia:
Iroquois historian Elizabeth Tooker has pointed to several differences between the two forms of government, notably that all decisions were made by a consensus of male chiefs who gained their position through a combination of blood descent and selection by female relatives, that representation on the basis of the number of clans in the group rather than the size or population of the clans, that the topics discussed were decided by a single tribe.