The Gorn had a reason to want the outpost gone, then they kept going

The Gorn's claim deserves to be taken seriously, but by my count Kirk ends up only about half right about them, and it's the less important half. The Gorn had a reason to want that outpost gone. They hit the defenses, then they kept going.

Kirk's change of heart about the Gorn rests on Spock saying it may well be possible

Kirk hears it clearly when he's told that mercy from the Gorn means a faster death. Back on the bridge, McCoy asks whether that could be true, and Spock's "ringing endorsement is that it may well be possible." As far as the episode shows, that's the entire evidentiary record for what comes next.

Kirk gets the upper hand, refuses to kill the Gorn, throws the dagger aside, and reasons that maybe the Gorn thought it was protecting itself. At the start of the episode, as far as I can tell, Kirk thinks the Gorn are butchers, and the evidence backs him. By the end, he thinks they were defending their territory. By my count, he's about half right, and it's the less important half.

From the Gorn side of the border, wanting the outpost gone is reasonable

From their side of the border, a Federation outpost appeared where it had no business being. To me, wanting it gone is completely reasonable. A warning, an ultimatum, even a strike on the outpost's defenses would all fit that grievance.

The Gorn hit the military targets, then kept going

The Gorn did hit the defenses, since the phaser batteries went first. Then they kept going. Nothing in the episode shows a warning or a demand to leave.

The outpost had real military targets: the batteries, and the weapons Kirk later pulls from the outpost to fight back. The Gorn could have stopped at those specific targets. As I see it, a border grievance explains why you'd want an outpost gone.

Do you think the Gorn's border grievance justifies how far their attack went?