The original Star Trek had, if not the greatest (I really cannot answer that one), one of the greatest affects on American society… at least the group that watched it and “got it.”
It taught its fans during the 60’s and up to look past skin color and differences. Kirk was kind off a run in and shoot ‘em up cowboy but there were episodes set in hypothetical history situations, dealing with difficult social issues by setting them in alien planets, and the first interracial kiss was seen on that program. Episodes like the one with the Horta showed that running in and killing a, to humans, unintelligent species willy nilly just because you want something they have is extinguishing an intelligent species and, in the show, they stopped.
I watched it on its first running and a number of times since. I know that it made me think more than once.
One of the things about Star Trek is it engaged young minds (and older) with the flashy stuff but Gene Roddenbery got the messages through without you really noticing. He managed to get these through at least one generation.
The Enterprise had an international, interracial, and interspecies crew. Another first. Having a Russian on the crew in the 60, in and of itself, was a ballsy move… think back to what was going on in the 60s. I am undecided as to whether having Chekov or Uhura (a black woman) on the crew was the most ballsy.