In 1938, great fear of extraterrestrial life first appeared during a radio broadcast of H.G. Well's "War of the Worlds". Something went off in the subconscious minds of thousands of people and they fled looking for a place to hide from malevolent aliens.
Later on in 1942, a mysterious object suddenly appeared near Los Angeles and the military went crazy trying to shoot it down. This was followed by "The Foo Fighters" who monitored both the allies and "The Axis Powers" aircraft.
Even before the crash at Roswell in 1947, the U.S. military was on guard concerning extraterrestrial activities. They made a point of recruiting many Nazi scientists after WW2 to find out what they knew.
Both the military and the general population were very afraid of anyone or anything from outer space. During the 1950s, "The Day The Earth Stood Still", "Forbidden Planet" and "Invasion of the Body Snatchers" were the best of that sci/fi genre.
Into this atmosphere of dread and confusion, the U.S. Government and military decided to put a lid on UFO information. This story is well told in a documentary entitled "The Secret".
Ahead of its time even for the hippies and the general population, Gene Roddenberry's Star Trek was viewed by sci/fi fanatics only. Yet, it laid the basis of how many of us view the universe today.
Star Trek in its many incarnations, certainly prepared us for unpleasant aliens who could do us harm. "The Borg" reminded me of the "Grays": Their lack of individualism, the need to incorporate another race's DNA into their own, and the hive mentality.
"The Hirogens" reminded me of the Reptilians and their to desire to conquer people who they considered game. In the Killing Game, the race is both associated with the Nazis and the holodeck which fits this species perfectly.
When new powerful extraterrestrials were discovered, the Star Trek crews didn't quake with fear and classify everything top secret. They met the challenge and survived.
Below is a "declassified photo" of an Hirogen: