Orcs are evil

Orcs are a fantasy monster.  While Tolkien may have standardized them as the basic low-level mook hounding the protagonists, the idea of the orc goes back millennia before.  The word "orc" is an Anglicization of the Italian word "orco", which is a kind of monstrous demon of Italian fairy tales that feeds on human flesh.  This is identical to "ogre" in classic French fairy tales, which became its own type of monster in the modern era.

The orco takes its name from Orcus, one of the Roman gods of the underworld.  Orcus was particularly associated with torment and punishment, and therefore also associated with evil and demons.  He was normally depicted as a giant hairy monster.