Although that statement was in the movie, I don't know if there was any actual science behind it or if the human powers invented it to legitimize their activities.... considering CJ's obvious initiative and technical skill, I would probably say the latter.
I merely remarked on the fact that most Prawns *were* actually quite stupid. You can see that from the way they behave, most notably with CJ's friend who, unlike his intelligent counterpart, is hard pressed to even understand what he is doing, much less to cope with the situation (he clearly is bewildered and doesn't understand what the humans want from him, which eventually escalates into him becoming violent, another sign of intellectual inadequacy as his violence stems from fear, not reason). The fact that they trade their technology for canned cat food is another sign that they don't really know what they're doing.
I actually thought the action sequences were well-interseprsed with the rest of the movie, and as the upper posts mention there are explanations as to why the aliens brought so much weaponry with them, all of which boil down to the fact that without FTL sensing capability (which the fact that CJ is forced to physically go to get help indicates the aliens don't have) they had no idea what they were going to find on Earth until they got here.
Hm. Here we have a species which has enough technological expertize to bridge the gap between the stars, a feat which requires so much raw power you could easily boil a planet or two with it, bringing guns along because they fear - what? They could just grab Mars and drag it into the green belt if Earthlings don't want to play.
The biggest plot hole of the movie is that it tries to anthropomorfize a race whose very presence on Earth suggests a level of sophistication so far beyond that of the human race any comparison would be pointless. A race which evolved to the point of mastering technology necessary for FTL travel is by that very definition so advanced humans wouldn't able to even present a disturbance, much less a serious threat requiring weaponry.
The sole redeeming point could be that most aliens are in fact, dumb worker drones, with only a few intelligent "commanders" present. But even then - why guns? They can bend the "immutable" laws of the universe. They can travel faster than light, manipulate gravity... do they really need something as crude as a hand-held weapon?
Do we need miniguns to deal with ants?