The culturally monolithic alien race seems like staple of science fiction. All members of an alien race dress alike, speak alike, worship alike, and hold the same beliefs and mindset. Consider Star Trek, for instance; pacifist Klingons not obsessed with warfare and honor, socialist Ferengi, and emotional Vulcans are extremely rare, if not unknown.
The monolithic alien culture is probably the result of artistic license; it’s easier to have everybody share the same mindset than to create distinct subcultures. My question for those more familiar with SF than me: has a fictional alien race ever been created which has a diverse culture, where there are different religions, different beliefs regarding violence and honor, different fashions, and different forms of music?