But I don't care about what a person did in the past. I care for what they are today and what they are going to do in the future whether they are real people or comic book characters. I don't care whether my friend grew up with very liberal and lenient parents, that doesn't justify him not respecting them or other people and authority. I don't care whether Batman's parents died or not because I don't care for the reasons for his actions, all I want to know is whether he is a hero now and whether he will remain a hero in the future and I want to know whether his actions will reflect that. I judge a person based on who they are, not what they were. What happened yesterday is yesterday's problem.
So, with Dante, telling me about his background isn't doing him any favors considering that I'm not caring about his past (especially since his backstory is the same as pretty much every other revenge character out there). What I want to see is the kind of man he is today and whether he'll grow up to be someone better in the future. It's the reason why I like Superman and Iron Man. Their pasts aren't a relevant factor in their lives, they do what they do because it is right and needs to be done. I just want to see whether Dante grows up to be a better person, that's all.
You're still looking at it as a justification (you keep using that word), when it's not. His past isn't a license for him to be a douchebag sometimes, it's just the reason why he's a douchebag sometimes, and this game focuses on him becoming what you wan him to be - a better person. It's called "character growth" for a reason, and it's always a much more intriguing experience when the character has to work through some sort of flaw, like Dante's jerky, hedonistic lifestyle. He's going to work through that throughout the course of DmC, and learn some humanity. It's been explicitly stated by NT for a long time. You keep complaining that Dante is a douchebag and that you "want to see whether Dante grows up to be a better person," and we're telling you just that! He's a douchebage because of his traumatic past, and he's going to grow out of it as the game progresses.
Even Nolan's Bruce Wayne went through this, when he wanted nothing more than explicit revenge on the man who killed his parents, and was chastised for it (Rachel slapped the sh*t out of him, remember). Later on, he learned that revenge wasn't necessary so much as justice itself was. Hell, even the classic Dante had little more motivation than killing every demon he came across "until he hit the jackpot sooner or later," eg, finally killing those that killed his family. Even looking at Iron Man, he did what he did because he was tired of seeing his products used to hurt people. The only person of the listed names that doesn't have any past to motivate them is Superman, and he is a very bland character.
When you're trying to craft a story, the last thing you want to do is create generic, two-dimensional characters who do stuff just because it's right. It's a wholly and completely missed opportunity for more character, and even world, development :/