でなくてなんだろう（か）If this is not X, what is?
This construction asks rhetorically what something could be if it were not the named category. The speaker is not seeking an answer but emphatically identifying it as that category.
How it works
The noun before the fixed ending is the speaker's intended conclusion. The question challenges the reader to imagine another label, while implying that no other label is defensible. This makes the construction effective for admiration, praise, accusation, and condemnation.
Admiration and criticism
The evaluation may be positive or negative, but it should be strong enough to justify the rhetorical question.
Not a real question
The listener is not expected to supply another answer. In the first example, the speaker has already concluded that the conduct is devotion; in the second, that the conduct is exploitation. The question form makes each conclusion sound emotionally undeniable.
Three different kinds of exclusiveness
にほかならない directly states that something is precisely a given identity or cause. The target construction presents a similar conclusion as an emotional rhetorical challenge. By contrast, でしかない often reduces something to “no more than” a category, while をおいてほかに ... ない selects the only suitable candidate from a set.
More examples
彼女が自らの地位を危険にさらして内部告発したことは、勇気でなくてなんだろうか。
What could her decision to risk her own position and expose wrongdoing be, if not courage?
Analyze百年にわたり守り継がれてきたこの森は、地域の宝でなくてなんだろうか。
What could this forest, protected and passed down for a century, be if not a local treasure?
Analyze事実を知りながら市民に沈黙を強いるのは、権力の乱用でなくてなんだろうか。
What is forcing citizens to remain silent despite knowing the facts, if not an abuse of power?
Analyze患者一人一人の声に耳を傾ける彼の姿勢は、医療の良心でなくてなんだろう。
What could his commitment to listening to every patient be, if not the conscience of medicine?
Analyze異なる意見を力で封じる行為は、言論の弾圧でなくてなんだろうか。
What is the act of suppressing opposing views by force, if not repression of free expression?
Analyzeこの映画が観客に過去と向き合うよう迫る力は、芸術の力でなくてなんだろうか。
What could this film's power to compel audiences to confront the past be, if not the power of art?
Analyze