Figured I'd be helpful, and give you some points for DB to make for his case against goodness. Since it's contradictory to your viewpoint, and complimentary to mine, I could lend some angles you might have missed.
1. Heroes are extremely condescending. They look down on people. always saving them. F-em. Let them save themselves. They need to take responsibility for their own lives. Super Heroes function on the basic presupposition that people are incapable of self-preservation. And that's simply not true. Case in point, lone girl walking through rough neighborhood late at night gets mugged. Honestly? Screw her. She should know better than to be there. I have a very small chance of being bitten by a shark this week. You know why? I live 60 miles from the nearest ocean. If you don't go where sharks live, you don't get bit. Swimming in the ocean is basically hanging out in their fridge.
2. You can not save them all. LB simply can't be in all places at once. Eventually, he will have to choose. Save this one, or save that one. But not both. No one should have the right to make that choice. What are the criteria for the decision? How is the choice made? Do you save the single innocent, or the bus load of guilty? This comes down to one of your own core beliefs, in that whichever one he chooses not to save, he basically kills.
3. Who decides who is "good" or "evil?" It's not always obvious at first glance. For example: A man is being chased by three others. They are going to beat the snot out of him, but they have no weapons, so most likely won't kill him. Hero time, save the guy, right? Well, what if the three dudes are chasing a child molestor they just stopped from raping some little girl? Should LB beat up those three, so the guy can get home safely? Sure, as a moral absolute, no one should beat up anyonme, but I happen to live in this could, harsh place called reality, and here, s- happens. The only way LB could stop those three guys is with a beating, and they clearly don't deserve it.
4. Heroes are hypocritical. "Don't beat people up, or I'll kick your a-." It's insane. Literally, it fits a clinical definition of insanity, believing that one set of rules apply to oneself, and a different set for everyone else.
5. Selflessness is dishonest. Humans (the super variety included) are incapable of pure selflessness. We only do something if we're gonna get something back. Even if the something is small and invisible, like the feeling of "having made a difference." Selfishness is the only form of honesty. The guy who walks up and takes your wallet is not trying to trick you, or misdirect, or fool you. He is honesly saying he values money more than your feelings or personal safety. Simple, honest transaction. The hero who gets your wallet back? He's saying 1: You are weak, and cannot do it on your own. I am therefore superior. 2. I have passed my judgement, and whatever need this man may have (his kids may be starving) is less important than my personal sense of right and wrong. 3. I know nothing about you, but have the belief that you need this money so badly, it's worth me risking both our lives to get it back for you. 4. You should thank me and be grateful, for I am wonderful to stop my day to get your wallet back. Even if he never says any of this. Even if he doesn't consciously think this. These are the implied beliefs behind his actions.
Some Pro-Darkness beliefs:
1. Life is hard, and that's a good thing. Survival of the fittest. Look, evolution is a test. If who you are is enough of the right answers on that test, you pass, and are allowed to pass on your worthy genes. If not, you fail, and die. A bit cold, but clean, honest, simple, and self-contained. The kid who swallows too many marbles doesn't get to grow up and have stupid kids of his own. But, the superhero business makes every answer to the test questions the right answer. Everyone survives, evolution stops.
2. Adversity makes people better. Overcoming difficulty shows you how to overcome more difficulty. In this modern world, where great dangers are somewhat unlikely, a man (Or what we are forced to call a man) faces the posibility of going his entire life without ever knowing if he is or is not a coward, or a wimp, or unable to defend himself. Sure, we save a few thousand lives every year, but we have sapped some of the meaning of Man out of it. This kind of goes back to number 1, but adds the point that you can grow as a human being. However, if someone does all the work for you, you will never grow.
3. Darkness makes you appreciate the light. If every day is a sunny day, then sunny days have no value. It is because of the rain, not in spite of it, that we have learned to value pleasant weather. In fact, with less contrast between what is light and dark, the slightest bit of grey becomes a bigger threat to us. If the biggest challenge of your day is whether or not you can find a pen, then if your car breaks down, that's a huge emergency. But, ask a Holocaust survivor how big of a deal a flat tire is. You may have a flat, but you're not being forced to do hard labor, fed eachother, and then gassed and killed horribly.
So, those are some points DB can make in his case against LB. Use what you will discard the rest.