Star Trek: The Next Generation, in many of its episodes, portrays and examines many social issues of the present day is such a way that the audience can come away with a new, non-emotional, understanding of the issues. Such portrayals and examinations are the provenance of science fiction.
An example of a social issue discussion appears in episode #117, The Outcast. In this episode the Starship Enterprise encounters the J'naii, an androgenous race for whom the concept of gender is so foreign that they find the concept repugnant and deviant (even though they do reproduce sexually). Those members of their race who demonstrate tendencies toward one gender or another are labeled deviant and perverted and must be "cured". Commander Riker, an officer on the Enterprise, finds one J'naii, Soren, very attractive, and it responds to his attention by realizing that it prefers being female to sexless. When her society discovers her desires it demands that she be cured of her perversion. Soren points out how similar she and those like her are to "normal" J'naii, and cries out, "What makes you think you can dictate to us how we love one another!" (ST:NG #117) Nonetheless, she is put through a brainwashing that convinces her that having gender is wrong, and she ends up claiming she is much happier as a "normal" J'naii, although her formerly sparkling personality now appears to be one of no personality at all. (ST:NG #117)
The parallels of the episode are clear to some attitudes about homosexuality in American society today. A society with no gender that considers people who announce they have a gender to be perverted is the same as a society with gender (male with female) that considers people that have a different view of gender (male with male, female with female) to be perverted. The J'naii's insistence that their "deviants" can be cured parallels programs in America that say they can "reprogram" or "cure" homosexuality. (Hadfield)
The Star Trek episode subtly condemns not only anti-homosexual attitudes (as exemplified by the J'naii's attitudes), but the idea of "curing" genetically determined behaviors and desires. (Khytam) However, because the discussion is done in a science fiction setting, the discussion is less likely to cause an emotional response to the issue in the audience than if the same issues were presented in a standard drama. Science fiction places its ideas in places and/or times that are separated from the audience's, allowing the audience to believe that the discussion isn't about them and thus doesn't trigger emotional responses. (Asimov) This allows the audience to have an intellectual appreciation of the discussion, unhindered by emotion. In such cases, the audience can begin thinking and arrive at reasoned, logical conclusions about the issue under discussion. In the case of The Outcast, it allows the audience to examine their own attitudes and prejudices about homosexuality.
Many ST:NG episodes dealt with social issues that allow the audience to think and arrive at reasoned conclusions, including what is the meaning of human, what makes a parent a parent, what is love, when and how does one become an adult, and many others. Because of this approach to storytelling, ST:NG demonstrates how science fiction can affect an audience.