And when the results did not turn out as they hoped, they were ready to force the Cairhienin to stop it. It was all or nothing for the Aiel. As we see in the case of Shaiel, all nor nothing does not work. She tried to go full Aiel, and died and lost her child to the infidel because she had not fully internalized their ways to the extent that made them workable. An adult wetlander is not an Aielman, and the adaptation you suggest, and which the Cairhienin attempted, which so offended the Aiel, is a healthy and necessary compromise, for which the Aiel themselves cannot see the necessity. They are willing to teach their ways, because they see it as right and proper, which is how Rhuarc describes it. They are not engaging in an equitable, equilateral cultural exchange, they are instructing the ignorant of what is the only "proper" way to behave.

The Shaido are an extreme manifestation of that mentality, and the Aiel might not succumb to the degeneration, but they still have the point of view of looters and raiders, not rulers or conquerors. They might treat the wetlands as something like the Russians under the Mongols or a similar analogue, whereby a foreign culture simply plunders and dictates the terms of their relationship, without care or attempts to make them work together or establish their rule, as the Seanchan do. That can only lead to friction between Aiel and wetlanders, and rebellions and other acts that would set their Aiel masters even more firmly against them.

Because the Aiel don't see alternative cultural ways as simple differences, but rather as shortcomings and moral or ethical failures, they are not going to be able to rule wetlanders or even live in peace with them in close proximity. Even Aviendha, the best-adjusted Aiel to wetlander ways, having moved beyond condemning their ways to just thinking of them as soft or weak. She as learned to adjust her expectations to perceive strength or character in individuals by their own standards, but still does not get the overall notion that differences are only that, and not violations of the only right way to behave.


If they lasted that long. The point is, even with Rand anticipating the cultural friction, there were still instances like Mangin's murder of the tattooed guy. Even Rhuarc did not get the reasoning behind Rand's punishment. All that held them in check was Rand's orders, and their blind obedience to him.
In a situation without Rand's leash, they'd be worse. Rand's own granddaughter envisions replacing the Seanchan Empire with Aiel hegemony. Their attitude of superiority leads naturally to that mindset. They have so much of an advantage in direct force that there isn't much room for thesis-antithesis-synthesis to take place. There simply is not much room for the wetlanders to push back against the Aiel.

Which is just another problem with them. These kind of aberrant and extreme behaviors can someday be switched around do make them dangerous again. They have to be 'destroyed' for their own good as well, so that remnant of a remnant has a chance to adjust and come into contact with other people, and interact with them, rather than holding themselves apart and superior. Whether the AoL Way of the Leaf or the Third Age Way of the Spear, they are simply choosing different forms of mental slavery to turn their consciences over to. They need to be broken as a people so they can move on to become regular people.