I mean, in a story sense it is only as absurd as it would be for your character and how you are playing them, a person doing a christian, low corruption liberationist playthrough, it would make perfect sense for you to side with the rebellion as is.
For more corrupt and ambitious characters, it is very easy to justify by pointing both to how moudable Aria is while she is in your care, and how you can effectively use her to represent your own interests as shown by installing her when low on willpower, or hell, if you get her corruption high enough, she further expands and entrenches the interests of slavery in Raana so you get all the benefits of installing a friendly puppet regime, while also entrenching slavery.
Hell, the whole manipulating Aria and using the rebellion for your own ends is a constant thing the detractors to your involvement with the rebels keep bringing up in game, people are well aware you can be doing that and that it may be your motive so it is hardly like the game is expecting you to be throwing in with the rebels out of ideological commitment alone.
And given Ikaanos starts out either in a decently piss poor and slowly falling apart state (normal start) or actively on the brink of falling apart completely (dying world start) it is easy to justify in character why you might want to overthrow the Adlers even without any particular ideology behind it, as under their stewardship everything is becoming more fucked, with little in the way of recovery or resurgence.
So yeah, while it doesn't make sense for every character to go with New World Order, I don't think it is inherently absurd given the numerous ways you can play the game, and your character.
