With the utmost respect to the good doctor I personally postulate that any alien beings capable of traversing the universe to come see us would have a) long-ago figured out ways around their visitations being lethal to those they visit and b) have probably matured as a species to the point of being above conquest of other civilizations and would instead be more interested in exploration and scientific discovery
I am however open to the alternative that he is correct
I do however subscribe to the Idea that while it is statistically *probable* that numerous other alien civilizations may exist close enough to our solar system for a visit... It is rather *improbable* that those civilizations meet both criteria of being close enough to visit us AND technologically advanced enough to make the trip.
See "Fermi paradox"
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