So as commenters pointed out last week, Kiritsugu has this unique ability to stow away his emotions when he pulls the trigger. It was this ability that allowed him to kill his father, and now his mother, without remorse.
I think that there’s a bit more to it though. Kiritsugu is a born pessimist and a bit of a coward. Would his father have actually killed more people? Perhaps. But if Kiritsugu had stayed with him, he could have enforced tighter security with the medicine cabinet.
Would the plane with the bees have killed half of New York if it landed? Maybe. But Kiritsugu could have done something else to prevent it. Why didn’t he have the plane land in the ocean? Then he could have gone in with his boat, knocked the wall off the cockpit, taken Natalia out, and then blown the plane to kingdom come.
Kiritsugu always assumes the worst possibility will come to pass. His mother says that he always does what he “should” do and not what he wants to do, which makes him inhuman.
I disagree. What makes Kiritsugu inhuman isn’t that he acts rationally rather than emotionally. It’s that he lacks hope. He always takes the path of least risk. How he killed Archibald and his wife, the way he hasn’t even revealed that he’s a master, everything he does is cautious and downright paranoid. He always assumes the worst will happen, and eliminates any possible risk along the way.
Eliminating every risk isn’t always the most rational strategy, either. Higher risk actions can have higher rewards, and sometimes the risk is worth taking. Compare Kiritsugu’s fighting style to Shirou’s in F/SN, for example. Shirou doesn’t kill his enemies after they’re defeated. (heck, he doesn’t even really want to defeat them) But by letting them live, they decide to help him, and that’s what makes him able to win the war. It’s risky, but the payoff is huge. Shirou charges head on into the thick of the fight, while Kiritsugu snipes people from the sideline. I’m torn on whether Kiritsugu always chooses the path of least risk because he lacks any hope whatsoever, or simply because he’s a coward.
Natalia’s plan was pretty dumb though. Why would you trust the airport security to catch bees? Why would they even care about bees? And can’t he just have them fly past the checkpoint and meet him on the other side?