A different spin, though...
Who is responsible for Cloud going nuts? The prime suspects are Cloud, Tifa, and Sephiroth.
For Cloud: He is the one who constructed this false persona business for himself. Thus, he is responsible for all its effects. QED.
For Tifa: She is the only one who could have possibly pointed out to Cloud his psychological charade. She didn't. (That's my theory behind what the voices in her head are saying when she falls in the Lifestream with Cloud in Disc II.)
For Sephiroth/Jenova/Hojo: They leave out the obvious truth: that Cloud existed before Hojo's project.
For Choco Billy: Because everyone needs to joke around sometime.
I think this question could even be extended to "Whose fault is it Meteor got summoned?" Since Cloud goes nuts and gives the Black Materia to Sephiroth, whoever made him go nuts indirectly caused Meteor. Personally, I think Cloud is fully responsible for Meteor (not just partially), because of all that Camusian crap.