Learn English – Word/Phrase to describe someone who wants ALL or NOTHING of it

I don't know of a phrase where someone can so generically point out a flaw. In your example, I'd say human - nobody is perfect. Perhaps his weakness or limitation would fit here.

There are words for dramatic flaws.

An Achilles heel: a portion, spot, area, or the like, that is especially or solely vulnerable. It does not need to lead to his downfall; it connotes someone who is pretty damned perfect except for this one thing. "Tom Cruise has an Achilles heel" would be understood that way.

His Achilles heel is his quick temper.

Shortcoming, or foible would be understood as an understatement; if he's crazy, that's a major problem; to call it a foible before stating the flaw would be mildly sarcastic.

A tragic flaw in drama is a failing of character in the hero (someone of high repute/honor/etc.) of a tragedy that brings about his downfall. Regarding Hamlet:

He has exceptional qualities like graceful personality and popularity among his country that is eminent. His tragic flaw is his delay in action and irresolution...

Other expressions for this are simply flawed, or inadequacy.

Since you're asking in a psychological context, are you looking for one of:

Detachment (detached)

Dissociation (dissociated)

Depersonalization (depersonalized)

Emotional numbness (numb)

Based on the updated question, perhaps you're looking for:

Nihilism (nihilistic): Nihilism is often discussed in terms of extreme skepticism and relativism; for most of the 20th century it has been associated with the belief that life is meaningless. Existential nihilism begins with the notion that the world is without meaning or purpose. Given this circumstance, existence itself–all action, suffering, and feeling–is ultimately senseless and empty.

From the Encyclopedia of Philosophy article on Nihilism, though there are plenty of other choices (e.g. Wikipedia).