The gist of the argument is that the Nigerians in the movie are presented as exemplifying many of the worst racist slurs against Africans. To be specific, their leader is presented as a cannibal and the women are presented as sexual degenerates.
While the movie does present the Nigerians in a rather unflattering way, it also presents the white folks in a rather negative light. There are the corporate types who care only for money and are willing to permit the most wicked deeds for profit. There are the evil scientists who are also willing to do anything. Is the eating of the alien flesh any more horrible than the experiments conducted upon it? And, of course, we have the brutal and violent military guy.
Interestingly, I suspect that most people would say that these folks are stereotypes of their roles (corporate bad guy, scientist bad guy, and military bad guy) rather than being racial stereotypes. After all, one might argue, you could have a black guy as the evil corporate bad guy, an Asian as the evil scientist, and a Hispanic as the military bad guy.
In reply, white folks can also take the cannibal role. When I saw that the Nigerian leader wanted to eat the aliens to get their power, I thought of the movie Ravenous. I also thought of Silence of the Lambs.
Naturally, it can be said that the cannibal stereotype is a racist stereotype specifically against blacks because of the history behind it. Of course, it can also be said that the evil corporate guy, the scientist bad guy, and the military bad guy are also racist stereotypes about whites because of the history behind them. After all, they stand for the alleged great evils of the white West: corporate evil, science evil, and military evil.
While folks will focus on the appearance of racism against blacks, the fact that the filmmakers also use the stereotypes of Western white evil might indicate that they are not racist, but merely lazy and unoriginal in regards to their secondary characters.
Another interesting possibility is that the use of such stereotypes was actually an attempt to make a point against racism. After all, the alien “Prawn” were presented as manifestations of many common stereotypes about blacks and other minorities (being stupid, violent, lazy, sexual degenerates and filthy). The Nigerians were also presented in the form of racist stereotypes as were the white corporate folks. Perhaps the movie was attempting to get the audience to think about all the various hateful stereotypes being presented. If so, the claim that District 9 is a racist film would be an ironic one.