Instead of focusing solely on the biology behind the prawns and Wikus’s (unbelievable) transformation (which must have involved the altering of his genes on a cell-to-cell basis), I’m going to talk about Wikus’s character in this blog post. I liked him as the protagonist. His personality was a mixture of douche bag and loving husband, such that I couldn't decide whether to hate him or feel bad for him. His character evolved over the course of the movie as well, making him that much more intriguing.
At the beginning of the film, Wikus was a lovable office nerd, appointed to a militaristic position by his father-in-law (in a move that stank of nepotism). It was difficult to reconcile the image of the bumbling cubicle farmer with the man who set shacks of prawn eggs on fire and sanctioned the death of two million prawns in one day. This all happened before we were introduced to humanized prawns and we only saw them as animalistic antisocial bug monsters, so we didn’t really care whether or not they died in masses. Later, though, when we’ve met Christopher and CJ, who have retained family love and a connection to the technology of their people, Wikus’s actions seem evil. Finally, Wikus ends the movie by killing what must be hundreds of humans in order to help Christopher and CJ escape to their mother planet. This might be construed as admirable, but Wikus only defended the prawn family because he needed them in order to reverse his transformation—so that he can return to his wife. Wikus’s one truly selfless act was to go back and save Christopher when he was wearing the mecha-suit.
I read Wikus’s function as main character as supporting apartheid. His idea of a resolution to the prawn problem is either separating them further from Johannesburg and placing them in tents or getting them off the planet entirely by fixing their ship and excising prawn-ness so that he can return to being fully human. If someone else was the main character—say, Christopher or one of the MNU guys—then the entire tone of the story would have changed. The main goal would then be either to save the prawns by getting them to a better place or to eliminate the monstrous prawns that pose a threat to the people of Johannesburg. As is, the audience can see that the prawns are thinking being that are being oppressed and yet no effort is made on the part of the main character to inspire understanding in humans of the prawn condition. This support of apartheid can also be read in the animalistic portrayal of the Nigerians as antagonists. Honestly, the film placed them almost below the level of prawns, because for some reason the Nigerians chose to live in the hovel that is District 9 and want to become like the prawns so that they can use their guns (just as MNU does).
I suppose the lame denouement was meant to expose the darkness of human nature and leave us with a bad taste in our mouths. In a way, the stagnant prejudices of the characters in this movie are more realistic than any major character change the film might have pulled out of nowhere. It would have been a miracle for the humans and prawns to like each other by the end of the movie, just as it would be a miracle for real racial tensions to dissipate in the span of a couple days.