There's always a boundary of cooperation. Like, the wolf pack that cooperates among themselves but fights other wolf packs for territory. Our closest neighbours in the animal kingdom, chimps, fight brutal wars between different groups. And, even among groups that cooperate on the surface, there's often cheating behind the scenes. Like, birds are well known for forming pair bonds that last for life but apparently adultery among birds is very common. The best strategy for a society may be cooperation, but the best strategy for an individual in a cooperative society may be occasional cheating if you can get away with it. Even plants compete for resources like soil and sun.

A computer model of a civilization might show that the optimum result is achieved with 100% cooperation. But, we aren't computer programs, so we need to find a society that's as good as possible given the constraints of our animal nature. It's actually pretty remarkable that we've created countries containing hundreds of millions of people who feel some sense of shared identity, and are willing to cooperate at least a bit with strangers from that same country.

On the subject of "reaching the stars", the space race is the perfect example of competition. There's no way that Sputnik would have been put into orbit, or humans onto the moon if it hadn't been for a massive competition between the USSR and the USA. Within those two societies there was a great deal of cooperation, but humankind wouldn't have "reached the stars" from cooperation alone.