He was a witcher. If Gaetan is killed: Geralt held his duty was to protect sentient beings from threats no others could vanquish - no matter whether the beings in question were cheats or saints. Gaetan had proven himself just such a threat, so Geralt paid no heed to his justifications and killed the fellow witcher.

Should you kill Gaetan Witcher 3?

If you're looking for the objectively best choice in terms of loot, we recommend sparing Gaetan. You'll gain 200 experience and be granted a new quest called Take What You Want. This will lead you to a stash of goods near Keira Metz' cabin, defended by some bandits.

Can Geralt kill Ciri?

9 CAN DEFEAT HIM: CIRI

She's not exactly a mutated witcher but her time and space manipulation powers are more than enough to put her in an even ground against Geralt. ... Even her book version could likely just scream Geralt to death.