…I feel like so much hate-based gasoline has been poured over this country planet that all it's going to take is one small match to set the entire thing blaze.
Maybe that is the reason we haven't been contacted by—or have heard transmissions from—any alien civilizations. Perhaps they all reach the point in their development that humanity currently finds itself, achieving an unprecedented degree of scientific enlightenment and standing at the brink of leaving their planetary cradle, only to have the technology spawned by that enlightenment allow bronze-age prejudices and hatreds—long simmering under the surface—to finally spew forth in all their base ugliness, causing the entire civilization to self-immolate.
I know that in the vastness of the universe, that couldn't have happened to every civilization, but I'm beginning to think it happens often enough that space-faring civilizations are very rare indeed and all their explorations reveal are the burnt-out husks of once-great societies littering the galaxies.