Thats not selfishness though. It isn't selfish to contribute to a group that benefits you. Its selfish if you contribute to a system that harms others because it benefits you. These are very different things.

In the various crucibles of civilization people came together precisely because resources were scarce. Yes they would eventually collapse when resources became too scarce to sustain whatever system they had built and infighting wasn't uncommon but resources are not scarce now. We produce enough food, we have enough homes, we have enough water (for humans not for our current technological setup). The issue we are currently struggling with is not scarcity its distribution. The technology produced by the capitalist era is more that sufficient to provide for us all.