None of the plot weaknesses described above are evident in the movie.
The only aliens the humans have identified are of a sub component of their race that cannot lead, cannot make decisions cannot do much of anything. The view the humans have of the whole species is based on the limited capabilities of these alliens. There is a hidden cell of leaders or technicians that are trying to extract enough of the fuel they need from the remains of other components that the starving, idiot masses of drones have mostly destroyed or do not understand. The leader aliens hid themselves for reasons that are made obvious in the film.
The remains that the leaders need to have access to in order to extract the fuel in minute bits, will not be in district 10, so they must act quickly to finish their project before they are moved.
The cat food addiction is like the low tolerance for alcohol that native indians had and how that was used by the european traders and settlers to incapacitate the natives they traded with. Why didn't the natives just wipe out the local hudson bay post and take the rum? Well they might have, but then you find out that the store is empty and no more rum is coming.
The rum doesn't originate in the store and lots of men with guns come after you do that.
Certainly though, people who do not like to think at movies will not like this movie much, or they wont understand what they are seeing. It doesn't tell you what to think like avatar does.
The concept in the movie, that the aliens are contemptible due to their own behavior and that they are treated like they are by the humans for very good reasons is an interesting and not very politically correct one.
