The obvious question in Pacific Rim is why do they use giant robots to fight kaiju?
Kaiju can be slain by conventional weaponry in the Pacific Rim-verse, even at the beginning of the Kaiju War when they were technologically on par with us. The problem was that even if the kaiju could be killed by conventional weaponry, it came with a huge cost in collateral damage. As it was seen in the movie, kaiju instinctively go to populated areas, and they are so huge that there’s really no conventional way available to stop them except for weapons of mass destruction. And obviously those kinds of weapons do not solve the problem of collateral damage.
So the Pacific Rim humans solved the problem with giant robots. The Pacific Rim Defense Force operation policy appeared to be to engage the kaiju outside of populated areas. The jaegers were big enough to physically intercept the kaiju and also the kaiju instinctively perceived jaegers as a threat so they could actually draw the aggro of the kaiju.
I suspect that the jaegers weren’t originally designed to kill the kaiju. I envision that the jaegers were supported by airplanes and warships, jaegers’ sole objective was to slow down the advance of the kaiju. What we see in the movie is that the jaegers were effective at actually killing kaiju on their own, which could explain why they aren’t heavily supported in the movies.
My point is, that you do have to suspend disbelief at some point, but I do think that Pacific Rim makes as much sense of its nonsensical world as possible.
(IMDB)
First Blog Part 1 
My ultimate argument for the Jaegers (which I talked about in my review) is a simple one, and one I have to use for a lot of movies: It was way cooler. Sure, the Kaiju could probably be toppled each time by large guns or cannons or bombs, but it’s far more interesting to watch and is way more fun to create giant robots to fight them. Those that disgrace the movie because the military didn’t just bomb the hell out of them don’t really know how to have fun.
The Rule of Cool totally stands as a reason to do things, especially when walking into a movie as silly as giant robots vs monsters. I do appreciate it when movies don’t rely too heavily on it, or at least when I walk away feeling like there are some pretty rational in-universe explanations for why things happen.
I agree, but most casual explanations work for me. One of the worst things a movie can do is get too bogged down in its own mythology and logic so I’m glad to see Pacific Rim mostly just skirted over the issue.