Spoilers below here!
So in my mind the movie is divided into approximately four parts.
The first part is from the beginning up until the drug packet bursts and she starts gaining powers. The second part lasts from that point until she confronts the drug lord in his den. The third part lasts until she recovers the drug packets. The fourth part goes from there until the end.
In the second part it quickly becomes apparent that Lucy isn't really in much danger from anyone. She can out-think, out-"guess" and out-shoot everyone else. She guns down probably a dozen of the drug cartel's goons. Then she finds the drug lord, mind probes him for the location of the other drug packets and then... lets him live.
The transition from part two to part three involves her leaving Taiwan to move on to the next part of her quest, but from that point on she never kills anyone else directly.
However in part three her mad dash through the Paris streets must have caused the death or serious injury of dozens of people.
That mad dash was an attempt to get to the hospital before the drug cartel goons, under the orders of the drug lord she neglected to kill at the end of part two, (re)steal and get away with the drugs, slaughtering at least a half-dozen doctors and police officers in the process. Too bad she couldn't get there in time to save them, right? Except she clearly doesn't care. She arrives, disarms the thugs, takes the drugs from them, then turns around and leaves. Leaving the thugs all still alive.
Then in part four she goes to the meeting with the scientists and the thugs follow her there and assault the building. She has already demonstrated that she can disarm and/or disable entire rooms full of people without even the snap of her fingers, and yet she tells French police guy to hold them off while she finishes her work. French police guy doesn't question the fact that she's not willing to take 30 seconds to fix the problem for them, or that she wasn't willing to kill or disable these same thugs before. And as a result over a dozen people are killed, many of them police officers/security guards.
So through part two she kills people left and right without a thought (including an innocent person who was in the hospital for treatment, but she decided his cancer was inoperable, so that's okay, right?) but then all of the sudden when she gets the chance to kill the drug lord and most likely prevent all the later deaths in the film, she chooses not to.
There is no direct explanation for this in the film. One possible interpretation is that as her mind expanded she suddenly had a moral or ethical breakthrough and decided she wasn't going to kill people anymore.
However i think it ties back to slightly earlier when she calls her mom while in the hospital. I forget if it's actually said or just implied, but it seems that as her mind is expanding she's actually losing her humanity. She was calling her mom to say she loved her while she was still capable of remembering what love was.
So under that theory she wasn't gaining morality or ethics or empathy, she was losing it and becoming completely amoral. At the point she confronted the drug lord she already knew what was quickly becoming apparent to the audience, that there was no human who could possibly be a threat to her. Once she'd extracted the information from the drug lord she had everything she wanted and she didn't care about him or what he might do to anyone else. (Not foreseeing that he would try to interfere with her attempts to retrieve the other drugs seems a little weird for a 25-30% intellect, but whatever.)
So a lot of people die because the almost omnipotent being just doesn't give a fuck if they die or not.
So given that in the end Lucy is portrayed as pretty much being god, and the recent article i read about the Gnostic influences in Snowpiercer, i started wondering how far back one could push this metaphor.
So in part two Lucy was clearly an old testament god. She would smite you if you got in her way, and occasionally you would get smitten for no good reason. In part four she was a middle ages crusading type god. She ordered people to go accomplish dangerous things for her with no promise of any direct help and not caring how many she was dooming on either side, and they just smiled and nodded and went into combat on her say-so.
At the end of the movie she has become a post-Martin Luther, kinda new agey, omnipresent god that everyone can have a personal relationship with.
And there are the extra tidbits about her uplifting
However i'm not sure if parts one and three work into the metaphor at all. Part one is before she has any power, so i'm not sure if that means anything. I guess part three kind of fits in with a new testament god, who's still willing to perform miracles in the world and in theory has become a merciful god that doesn't smite everyone left and right, but despite that isn't willing to do much with those miracles to actually save anyone either.
I'm not really great at coming up with metaphors on my own, so there's probably some more subtle stuff i'm missing.
1: The French guy comments something about how putting all the people in the police station to sleep was amazing, but we never saw him stop to check vitals on any of them. I was thinking it would be rather amusing if it turns out he was just assuming they were asleep and she'd actually just killed them all. "Yes, it was very impressive how i put them all to 'sleep'."