The thing to think about is that District 9 was taking a severely anti-human approach to sci-fi. It drew a lot of attention to a stark divide between humans and prauns, to the point where it's almost insultingly misanthropic!

This is embodied in Wilkus himself and his metamorphosis to one of the prauns. At the opening of the film, when he's completely human, he's a complete and utter wanker. When he's infected, and slowly begins to change, he becomes more sympathetic. Ultimately, when he's past the tipping point and exhibiting more and more praun-like qualities, he becomes almost heroic. It can't be a coincidence that the less human he became, the more sympathetic and likeable he was.
Then there's the portrayal of two family units and the quality thereof. On one hand, you have the praun family of Christopher and his son, and on the other you had the boss-man of the MNU and his daughter. It doesn't take a rocket surgeon to decide which was the better, more nurturing relationship.
I really,
really love how they did it. It's not often a movie gets me really hoping for humanity to get a kick in the ass by big honking space-guns.