Cultural diversity within various species

[f14peter]

Star Trek "Truthers":
"The Earth-Romulan War was inside job, man. Vulcans can't melt steel beams! The Federation is putting root beer in our tap water to control our moods! Gagh is made of Klingons! Gorn are lizard-people! Wait, that checks out, nevermind."

And the chem-nebulas: They say they're just a natural occurrence, space dust and all that, but we know better ... Mind Control

 

[Qonundrum]

You should check out the Doctor Who story "The Keys of Marinus", it's one of the few examples of sci-fi showing a planet with more than one distinct culture/society on it. It's from 1964 so it might bore, but for 1960s standards it's quite underrated... (for budget and narrative reasons, and limited time allotment, one planet = center for one society is easier on the audience to keep track of as well... that's why it's rarely done in sci-fi, or that's my reasoning for it anyway.)