I find it weird how your takeaway from the experiment is that the rats cared more about population maximization than well-being, when what the experiment showed was that the maximization of the population led to a decrease in well being and the rats therefore culled their own population.
My takeaway is that rats a kinda dumb, and think mating is a pleasurable act. They will mate until a point where their population is so high that it gives them severe displeasure and they will therefore stop the population trend to ensure their own well being.
Also I don’t think humans are much different. If contraception wasn’t readily available we would have a lot more kids.