When the monsters of the world continually get away with murdering innocent people and destroying lives, it is cathartic to see them finally get their punishment.
In this case, a bullet to the forehead was Parsa's final reward, offered up without hesitation by Gibbs.
The intensity of the last Parsa chapter in NCIS Season 11 Episode 14 can't be overstated.
It was hard to watch the Navy Seals storm Parsa's compound through the various jittery helmet cameras: it forcefully brought to mind the takedown of Osama Bin Laden. This was one of those times when it was easy to forget that this was a TV episode and not real life: there was real worry for the Seals as we saw them hunting through the darkness for their "jackpot." And real relief, too, when they announced that they had him.