The Sallis solution.
I propose a novel solution to the Fermi Paradox. It is typical for people to envision sentient alien species as monolithic, as monoracial populations – think of the “alien grays” who are portrayed as phenotypically fungible. What if this assumption is incorrect? Perhaps racial diversity is the rule among sentient species; thus, highly divergent human racial types find their counterparts in significant racial variability among the alien peoples inhabiting worlds unknown. I further propose a Gresham’s law of universal racial diversity: the more intelligent and productive races of any sentient species will tend to be demographically outcompeted by the more stupid and useless races; the latter, despite their deficiencies for proximate values, are inevitably more fit with respect to the ultimate criterion of survival. The threshold of technological competence for a detectable alien civilization would no longer obtain as the race or races capable of maintaining that civilization are replaced by those incapable. Therefore, no such civilizations are detected.
So, perhaps, a gracile and intelligent space-faring light gray alien race has been demographically replaced by a brutal and stupid dark gray race, the members of which are swinging from the trees among the ruins of a collapsed Dyson sphere civilization. The same would hold for other failed alien cultures, and if human civilization collapses, the likely cause would be similar.
And so it goes…