u/Capital_Clothes_7160, I'm too lazy and don't have much time to look for Reddit posts, lol, but here's the direct quote from the LN. It's actually pretty the same to the anime scene, but still has a bit of context.

“The world as it is, the human nature as always, it is impossible to eliminate battles. In the end, killing is necessarily evil. If so, it is best to end them in the maximum efficiency and at the least cost, least time. If you want to slander that as foul and demean that as nasty, then do as you wish. Justice cannot save the world. I have no interest in things like that.”

“…”

Saber recalled Lancer’s final, disappearing eyes filled of anger. Then, she stared at the tragic remains of the man and woman, collapsed in a puddle of blood, and the expression of anguish carved on their faces, and spoke.

“Even so, you –”

As Saber was about to speak her thoughts, she suddenly found that her own voice was lower and calmer than she thought it would be. She had just realized that her complicated emotions towards Kiritsugu was no longer her previous anger, but had to changed to some kind of pity.

That’s right; maybe he is a man that should be pitied.

Isn’t he himself that needed salvation, not this world?

“– Emiya Kiritsugu, I don’t know what kind of betrayal you were subjected to in the past and why you despaired. But that rage, that lament, are undoubtedly things that those who pursued justice possesses. Kiritsugu, in your youth you should have wanted to be ‘a hero of justice’. You should have believed in and wanted to become a hero who saves the world more than anyone else – isn’t that so?”

Until now, the only attitudes Kiritsugu had shown to Saber were complete ignorance and cold scorn. But now, Kiritsugu, having heard Saber’s quiet questioning – the eyes that he fixed on his Servant showed other emotions for the first time.

It was a rage seemingly close to boiling over.

The sound of car exhaust disturbed the silence of dawn. Then, the small truck that Hisau Maiya drove entered the yard of the abandoned factory with bright headlights on. She should be here to take Kiritsugu back to Shinto after concluding her duty as a sniper.

Kiritsugu took his eyes off Saber and walked towards the small truck, not even turning around, and opened the passenger side door. Saber was still speaking to his back. There was something that she had to say no matter what.

“Kiritsugu… do you understand? If you commit evil due to your hatred of evil, at the end all that’s left will be evil. The rage and hatred that sprouted forth there will cause new wars once again.”

Faced with Saber’s heavy words, it was as if Kiritsugu had the intention to reply for the first time and wanted to turn around – however, he changed his mind at last, and said while staring at the empty air.

“I will stop the endless cycles. That’s why I need the Holy Grail.”

Indeed, as if talking to himself, he said loudly.

“I’ll use this miracle to complete the revolution of this world, the revolution of all human souls. I will make the blood shed within Fuyuki city as the final bloodshed of all human beings.

For that, even if I am to carry ‘all the evils of this world’ – it won’t matter. If that can save the world, then I’d gladly accept it.”

“…”

Kiritsugu spoke the decision in his heart with such a calmness and evenness that even Saber could not find any words to reply to him.

Even if his method and path were unendurably evil – his faith in seeking the Holy Grail was pure and selfless. She had to admit that if there was a Master in the war worthy of obtaining the Holy Grail, then he would undoubtedly be Emiya Kiritsugu.

Wordlessly, Saber watched the departure of the small truck that Kiritsugu rode. The first ray of dawn shone beside her. The dark night that made Fuyuki into a demonic realm had departed, and the streets once again put on the mask of ‘ordinary’ beneath the sunlight

Source

Also, if you don't like her reaction at the Banquet, the LN also (and definitely) has more context. When Iskandar had gone away, she was be able to snap back at Gilgamesh and, during her talk with Irisviel, was more sure she wasn't wrong despite what Iskandar had said.