What makes #StarTrek effective in its social commentary is its creation and then gradual corrosion of social stereotypes.
The Klingons, the Vulcans, the Borg, the Kelpiens, the Cardassians - it is at its most effective when it builds a powerful stereotype and then tears that stereotype down through the lens of individuals. Worf's love of Alex; Spock's humanity; Hugh the Borg, Kelpian Vahar'ai, Dukat's softening - these are all exceptions that disprove the rule, and thereby reflect the most effective counter to discrimination - experience.
This makes Star Trek not just progressive, through its accommodation of these differences, but liberal, through its embrace of both the strength of diversity and the individual's insight that transcends it.
Christ I'm such a geek.