Evolution defaults to aggression as that is how it squeezes out fitness, and cooperative behavior is continually at odds with that and only seems to survive on one level up every so often, where evolution just starts treating it as giant agents anyway and the cycle starts again at a higher level. Similarly, we humans still have countries and borders and are only cooperating one level up. Cooperation is still merely being used as a survival tool, rather than an end in itself.

I.e., two people working together are working against another two people, those people if they somehow manage to combine are working against another collective, multiple collectives may combine and then work against other collective, etc... such developments may potentially be worse than just individuals fighting each other.

Similar to the idea that in a first contact situation, there may be an advantage in shooting first, and that often also implies only one iteration. I think shooting first is the default, and needs to be actively fought against.

Cooperation is not the default or preferred state for evolution, even though it's more efficient. To get there, it takes a lot of suffering and bloodshed. A few thousand years AI-caused suffering before it figures out that cooperating is useful more than one level up (if it ever does, as humans have failed so far) is not really what I have in mind when I talk about cooperative ethics. Cooperative ethics should be fundamental, not derived from short-term RoI computed in the moment.