Fate/Zero

[Buffalobiian]

Sure, Kiritsugu is someone special, being able to kill his inner representations of his wife and his daughter

You're making them sound like "illusions" David, while what they are are representations of the chances of having his wife and daughter back. He literally crushed the last one.

Since he didn't know about it, it could only be a deception...

Not necessarily. Gilgamesh admits himself that he owns more treasure than he knows. His conclusion is actually the opposite of yours: If it's a treasure that exists, then it must be mine already. He doesn't care for the grail since it's his, but he does care that other people are taking his property, so he'll defend it.