Things we are asked to believe in District 9:
1. That rich, beautiful, affectionate Tania would or should have ever fallen in love with Wikus in the first place, since he is a contemptible weasel and remains one throughout the film.
2. That a piece of machinery could fall off a spaceship that is hovering over a major urban center and presumably under nonstop surveillance by both governments and media, plummet to earth (straight down or nearly so, because, you know, gravity), and yet somehow disappear from human knowledge.
3. That alien rocket fuel is also, coincidentally, a powerful mutagen that converts humans it comes in contact with into aliens.
4. That a systemic conversion of a human organism to a completely alien one would not kill the original human organism and would leave the brain sufficiently untouched to preserve personality, knowledge, and intelligence (seriously, this is on par with the Independence Day “let’s upload a virus!” gag).
5. That the aliens, who are sufficiently concerned with other species’ use of their technology to make all weapons genome-specific and unusable to humans, would allow the Achilles’ heel of this mutagenic rocket fuel to exist.
6. That millions of aliens, whose leadership caste appears to have disappeared, would develop no alternative hierarchy for interacting and communicating with the human world.
7. That aliens, who are oviparous, and who according to the special features are hermaphroditic, conveniently have physical features compatible with human genitals that enable them to receive pleasure from female prostitutes.
8. That cat food, which is made of meat and meat by-products, is uniquely appealing to alien palates, so much so that it trades at a price an order of magnitude higher than plain old meat. Because we couldn't just have the aliens eat plain meat, that's not "ew-gross!" enough.
9. That aliens capable of interstellar flight are incapable, even over a 20 year period, of being conditioned to interact non-violently and productively in human society.
10. That these same aliens can be conditioned to engage in market transactions and comprehend spoken and written English.
11. That aliens whose language is comprehensible to humans would nonetheless be a completely otherized mystery to outside academics, researchers, and aid workers, such that no clear account of their history, goals, social structure, or needs would be conveyed.
12. That a spaceship full of aliens and vastly powerful alien technology, if parked over South Africa, would somehow be controlled by South Africa, with no intervention or horning-in by the USA, China, India, Russia, or other foreign governments, such that the only foreigners trying to sneak alien technology would be Nigerian crime lords.
13. That aliens incapable of conditioning to nonviolence, but in the possession of said vastly powerful weapons, which only they can use, and not inhibited by any kind of social structure, would confine themselves to fisticuffs.
14. That an alien who has demonstrated strength, speed, and reflexes far in excess of human limits can be confined and immobilized by a single human mercenary, if he is the really mean boss-man. (Also seen on Buffy the Vampire Slayer.)
What is “Christopher Johnson”? A former pilot or engineer? A self-taught scientific genius? Is it of the same caste or subtype as the “worker bees” that form most of the District 9 population? Why has it or another similar alien not made contact with any human agency? Is it really possible that the evil South African government could so effectively vet access to aliens that no outside contact could be made? Why is it attempting to accomplish the massive project of recovering potential or actual alien rocket fuel with such limited assistance? Are any other aliens than those we saw aware of this project? If not, why not?
If the aliens are both male and female, why do they take masculine (human) names and pronouns, even when conversing privately? Is there any reason why this movie could not have been about a female alien and her daughter? Or even a non-gendered being and its offspring? Why impose a “father/son” dynamic for no reason?
I spent most of the film hoping Wikus would kill himself and save everyone else the trouble.
Often SF movies or books are the product of someone who had a great what-if idea. What if alien refugees came to earth and we treated them like the most despised of human refugees? But the what-if is useless if the premises keep changing. The concept of the alien needs to be internally consistent and make sense, otherwise the intellectual, emotional, and political reactions to the events unfolding are less a natural outgrowth of the situation and more obviously driven by conventional moviemaking needs, i.e. we want some stuff to blow up real good and for the aliens to be intimidating at first but then sympathetic, etc. Most of the parts that don't jibe are obviously present so the director can hew more closely to the apartheid parallel. Combining didacticism and disrespect for your audience's intelligence is a sure-fire way to tick me off.