I thought he was already that way and it doesn't take much to cross the line anywhere in the sand.
Hell he already took out a motherfucking building for one guy, what is so hard to do what he did in this. But in that, he has evacuated everyone, so you can see he weighs heavily on innocent lives, as when those who are not in the battlefield do not deserve to die, and if they do, they do so at their own peril (such as watching Caster-Cthulhu in action and getting involved in it like those pilots.)
His is a sense of justice quite like poetry, it does not convey any sense of balance, but rather... a steep edge slope into an abyss of emotionless calculative perfection. If there was a God in my moral and theological belief, that God's personality would be very much like him. He does not force his ideals, there is no honor, as much as there are any chilvary... it is just child's play and Kiritsugu has progressed way beyond that stage... he is in what I call 'enlighten' to see the world as it is, a dark hellhole, he wants his piece of the pie and he has no reason not to commit his evils, and yet his reason is surely itself just.
He is in a sense... beautiful.
in a Hannibal Lecterish kinda way, but even that would be an insult, he is... probably way scarier, while people ponder on scarce and petty issues like knights honor and trying to win the fight, he wants to win the fucking war, capture every POW, torture them, set fire to them, make their country sign a tribute delivery every 3 months, and ensure his own citizens get PR whenever they migrate and have human rights at the same time... he will trample your shit, and all for the common good of everyone except himself and those he view to be his stepping stone to his ultimate goal.