I think the comparison falls apart a little bit because Dexter knows he’s doing something wrong, the moral environment he chooses to exist in is a half-assed excuse to quench an insatiable thirst for murder. Any sense of justice is a convenient excuse, instilled by a father who wielded Dexter as a weapon against his own frustrations. Dexter and his father hide his “real” identity because he’s weak, not because he’s strong. He’s a victim of his own mental illness and delusions, and fears that his hypocritical sense of justice will be his undoing. On several occasions he defies his ideals to cover his own ass.
You can certainly find versions of Superman’s story that fit similar scenarios, there are endless variations at this point, but I’d say his sense of justice is much less delusional. He could choose to watch from the heavens and kill unabated, but instead he goes to great lengths to try and live like everyone else does, and generally adheres to the same shared sense of justice (shortcomings and all). He typically struggles to kill even his worst enemies, and will go to great lengths to sacrifice himself to avoid it (a familiar christian story, of course).
