The movie did take a turn towards more character-based elements, but even then I felt it hard to feel much emotion for the characters. Wikus starts out with a compassionless, almost sadistic view towards the prawns (doing things like laughing at the sound of the prawn nest being exterminated), and then he refuses to kill one of them when they're testing the weapon? Kind of a non sequitur. I also found him pretty annoying in general. My dislike for Christopher stemmed from his overly-human characteristics (such as his wide array of human emotions) and the fact that he moved the story towards the cliched 'I have to save my people' angle. Really lame.
Spoilers be ahead.
I found that (as the example you mentioned: nest extermination) was a great character device in that it shows just how well received the prawns are to the general public; I mean, Wikis is put in charge of moving this entirely sentient species to a new location not because it would be better for them, but to get them out of the human populations damn hair.
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The fact that Wikis refuses to kill the prawn, to me, is not as "damned from the source" as you may think it is. His refusal is due to the extreme experimentation that he is going through, and although he didn't view those egg sacs as anything qualitatively sentient, he certainly was able to recognize the fact that he was taking an adult/mature life - but what also takes precedence in that situation is that he is not acting as a man, but as a test subject.
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This is where we definitely deviate on Wikis/Christopher as characters though. Wikis to me is about as compassionate as Longshanks from
Braveheart, though without any of the tact, guile and... well, brains (i.e. he is a moron). Wikis does nothing through the movie that does not serve in his best interest (e.g. running away from Christopher when he acquires the mech suit), in fact he only gains the lead management position due to his wife's father. Christopher on the other hand, was completely self sufficient as a character - all the things that went wrong in the movie was because of the humans and because of Wikis. Hell, he planned on saving his people since they were stranded (humans wouldn't let them leave). Had not anyone intervened, he would have never lost the black liquid, he would have a hell of a lot less dead prawns on his conscious, and he would have gotten to the mothership to take off to where he needs too. Christopher's story has always been about helping his people.
I hated Wikis as a character; however, I am of the firm belief that you are supposed to hate him, he represents every fallacious bullshitted wanker to walk the planet. Not only can he easily showcase his ability to be sincere and love, he can be bestial and filled with ill will. He
is bigotry.