That's a good point - I think when it comes to stories for adults, using a narrative tool like replacing the humans with animals or setting it in a fantasy or scifi setting can help people appreciate it more honestly. Kind of like how Battlestar Galactica can openly discuss the morality of violence against an occupying force, while if it was set in Iraq viewers would have been much less open minded to examining the concept.
Perhaps its adults books which should replace humans with animals?
As in the example you pointed out, this is a very common trope in SF. Often aliens are used, rather than animals; a recent well known example is District 9. Or my favorite example (in film), They Live.
I don't think I agree. Many non fantasy non scifi books go there and adults get them. Irak is politically charged sure, because there is war right now and people support that war. That does not exclude fictional place, whether historical or current.
In particular, people who read historical fiction deal with these topics all the time.
Stories about German occupation, whether real or made up deal with it. French revolution is all about violence.