Lots of fantasy (and other fiction) revolves around or has some involvement with warfare, and decides to go for a fodder race.
Fodder races enable tons of guilt-free violence because the enemies being killed are literally subhuman, or the walking dead, or aliens who don't really count because they're horrid.
They don't have to be non-human, though. In Star Wars the stormtroopers (the name itself is a nice nod to the Nazis, the group of humans that can be killed with minimal bad karma in recent history) are all masked. In fact, they're covered from head to toe in armour, which nicely dehumanises them. It's later revealed that they're all clones anyway, which may (for some) reduce their humanity, as they're essentially grown for the job rather than being an individual with freewill.
Orcs and goblins, most famous in The Lord of the Rings, just have the appearance of humans that have been smacked very hard in the face with the ugly stick. They also tend to seem rather bloodthirsty and perhaps be a bit thick. Although we like to pretend not to judge books by their covers (covers are arguably the single biggest factor people consider when buying a book, incidentally) we still prefer attractive people to ugly bastards (after all, that's basically the definition of what being attractive is). In Ancient Greece Phryne, a famous beauty, was put on trial in Athens and her lawyer offered a novel defence. He stripped her naked and asked who could condemn someone who was so clearly Aphrodite's handmaiden* (great beauty being considered a gift from the gods). She was found not guilty. In the same way, Galadriel is renowned for her beauty, whereas the Uruk-hai are not.
Zombies are probably the most hackneyed modern fodder race. The walking dead, with a weird sort of virus that reduces them to feral animals and who can infect others with a bite. I'm not that into zombies (although I do like The Walking Dead and The Last of Us looks promising). The USP of zombies is the emotional connection. It's similar to vampires, the Borg, the cybermen and playing golf; that terribly gnawing fear that one day it could happen to me. Plus, it can happen to close relatives and friends, as a fate worse than death.
Then we have aliens. These aren't evil necessarily, of course, but their inhumanity can make them a nice fodder race. Ugliness can sometimes indicate whether they're wicked or not (compare the Jem'Hadar to the Vulcans) but this needn't be the case. Unlike zombies and the often stupid orcs/goblins aliens can not only match human intelligence, but often exceed it. A slight problem is that an actual alien idea is quite hard to come up with, so most of them end up being really very similar to us (two arms, two legs, a torso, liking war a lot etc).
The potential problem with fodder races is that it makes war a bit black and white. With the possible exception of WWII (the Nazis and Japanese PoW camps were not exactly nice) most wars tend to be morally grey. I think that a fodder race and clear dividing line between right and wrong in warfare can not only be a bit simplistic, it can also miss an opportunity for the author to explore moral ambiguity.
*That delightful snippet of ancient history is from Philip Matyszak's Classical Compendium.