Superman had not yet developed a code against killing, but he DID take advantage of the fact that no one had seen a man with these powers before, making his bluffs all the more powerful. But even in Action #1 ("The Reign of the Superman" is NOT the same character) it states:
Early, Clark decided he must turn his titanic strengh into channels that would benefit mankind.
That's the beginning, folks. Yes, when he is going after a munitions broker fostering war in Latin America to spike sales, he doesn't ask for permission from the State Department. That doesn't make him an outlaw!
Of course, everything changed during WWII:
I wouldn't call that dark, though. Actually, that's kinda cool!