Ruin Explorer
Legend
Orcs fail as a representation of human evil because you can always excuse or put aside their evil on the grounds that they're doing it because they're orcs, and it is somehow "in their nature", rather than in human nature.It doesn't seem to me that you can argue that orcs are a representation of human racism, but not a representation of human evil. Either they are a separate species that does not represent humans, or they are capable of being a representation of humans, including human evil.
Orcs frequently become representations of human racism because human racist tropes are often used to describe them. Very often the exact language used to describe orcs, and the ideas around them, are identical to ideas about Black or Asian people (or other "non-white" groups) in the 20th century and sometimes even the 21st - especially recently - (or even if we go far enough back, Roman ideas about Celts* and Geats/Goths, albeit those ideas never got quite as extreme).
* = For a specific example see Cicero, who advised a friend never to buy slaves from Britain, because British people were in Cicero's opinion, so profoundly stupid, they were the only people who literally couldn't learn to read, and were in general the stupidest and ugliest people on the planet. Caesar's opinion was not dissimilar - he was convinced Celts were incapable of learning music, among other things.