It surprises me that this line elicits the reaction described. Surprising because it’s rather clear from the narrative that Superman is at his lowest point of anguish and disillusionment due to Lex’s machinations and manipulations. So his response seems entirely appropriate and entirely human, given the dramatic context. (After all, even Jesus — in his darkest moment — succumbed to an uncharacteristic expression of despair: “My God, my God, why have you forsaken me?”)
Moreover, and just prior to his self-sacrifice, Superman tells Lois: “This is my world. You are my world.” This would appear to indicate a reassessment and repudiation of his prior statement. (Typically, you don’t fight for a cause you don’t believe in.) Thus, the apposition of the two sentiments — especially given the similar phrasing — seems quite deliberate.