4. "Chimera" — Star Trek: Deep Space Nine

Original air date: Feb. 17, 1999

Each Star Trek show had a character who acts as an outsider to humanity or to the human-ish characters that dominated every crew. On Deep Space Nine, that character was Odo, the titular space station's chief of security. Though he could take any shape—a mouse, a chair or, most often, a six-foot-tall security officer—Odo's natural state was a big puddle of goo. Because of the more pessimistic world view of DS9, the writers never allowed the perpetually grumpy Odo to overcome his sense of alienation from all the other characters, who had permanent solid forms full of bones and organs. In "Chimera," Odo meets Laas, another of his kind, and invites him to spend some time on DS9. The two engage in the semi-sexual activity of "linking," melting into the same puddle. While Odo is quietly uneasy around other people, Laas shows open disdain for "monoforms," as a preemption to their petty fear of anything markedly different from them, and Odo begins to see his point. Laas transforms into a fog spreading over the station's promenade. Though the crew is annoyed, Odo says Laas is just changing forms, as changelings do. "Well, can't he 'be fog' somewhere else?" asks Chief Petty Officer Miles O'Brien, the show's everyman stand-in. His reaction echoes the sentiment of everyone you know who is ostensibly "OK" with gay people, but recoils at seeing anyone actually acting gay. Odo realizes that by spending most of his time as a bipedal humanoid, he is engaging in what, in sociological parlance, is called passing: dropping every attribute of his own cultural group to be accepted into another. In case there was any confusion around the metaphor, Quark, the Ferengi bartender, warns Odo, "This is no time for a Changeling pride demonstration on the promenade." Also, two Klingons decide to commit a hate crime.

5. "Stigma" — Star Trek: Enterprise

Original air date: Feb. 5, 2003

Enterprise, the final Star Trek series, is the first in the franchise's internal chronology. It was set a century before the time of Kirk and Spock, on the very first spaceship called Enterprise. Back then, Vulcans were surprisingly redneck. In "Stigma," TPol, the ship's curvy Vulcan first officer, tries to hunt down information on Pa'nar Syndrome without letting on that she suffers from this highly stigmatized ailment. Pa'nar is spread through mind melds (that thing where Spock reads some screaming dude's thoughts by placing his fingertips on his forehead). Back then Vulcans considered melds an "unnatural activity" practiced by a detested "minority" of telepaths. Thus, finding a cure was not a priority. The fact that T'Pol contracted it through a forced meld a season earlier matters not to the dick-ish Vulcan authorities she encounters. Though it came 15 years late, "Stigma" is a parable for the story of AIDS in the '80s with the Vulcans in the role of the Reagan administration.