What bugs me the most about "Arena" was that the story suggested that maybe Kirk and Co were in the wrong.
I mean really, the Gorn attacked the outpost, slaughtered EVERYONE there including defenseless colonists even though they had surrendered.
Then they lured the Enterprise there with a false message so they could kill them too.
I'm sorry, but that isn't exactly the most proportionate response to folks encroaching on your boundaries when you're not sure these folks even KNEW you existed in the first place. Kirk would've been fully in his rights and duties as a Starship Captain destroying the Gorn.