But its not obvious that imagining violence has no relationship at all to desiring violent things.
We imagine the fantasy violence because we like the fantasy violence. Normally it's cathartic for other problems than "I desire to ethnically cleanse ethnicity X, but the War Crimes Tribunal would prosecute me" - just the stresses & strains of everyday life as a student, employee, businessman etc, combined with normal human fight/flight reactions. Same reason we like fantasy violence in movies, books et al, and have done for thousands of years, judging by the Iliad.
I think violence in RPGs is a different question from inherently-evil-needs-killing-race in RPGs, though. And I do think Tolkienian Evil Races combined with (post) Gygaxian Naturalism can make me feel a bit icky sometimes. I'd tend to prefer enemies as truly inhuman fiends, like the things in The House on the Borderland or the enemies in 'Diablo', to Orcs who sometimes seem uncomfortably like Red Indian analogues in the D&D Western.