IMO it boils down to a matter of perspective. Like in the Cultural Revolution of China, you can divide people that look the same and have the same culture simply over the profession of their parents. Children against parents, even. You can divide people over the blocks they live on. But, the moment we are invaded by aliens, we share a powerful unifying perspective.

I personally believe (as I think you allude to below) that our politics, institutions and other power structures, have grown to depend upon (or started that way) institutionalized perspectives of division, and that they perpetuate these perspectives to their advantage by supporting whatever feeds them. I believe this is done with good intentions, bad intentions, and ambivalence. I also believe it is done both purposefully, unintentionally, and without reflection.

IMHO that's how so many seem to be able to cast aside these assumptions when interacting one-on-one, but cannot make the leap and approach greater society in the same way. We are trained, and we train each other. Who would create the notion of a 40 hour work week de novo?!

I strongly believe that when we focus upon our intellect, creativity, achievements, wonder, and our bittersweet human condition, we undermine perspectives of division, in favor of these powerful unifying perspectives that resonate within us all.