Should've, would've, could've.
Dog's story is about how anyone can turn their life around. He doesn't glorify what he's done in his past. He hates his past and continually tries to make his life better; and along the way to show others how they can as well. If it weren't for his past, most of these lowlifes wouldn't listen to him because they would feel he didn't truly understand them. He may not be a good role model for the Dudley Do Rights (are there any of those?), but he certainly is for anyone who has made a mistake and wants to change.
I don't remember the comparison you made between Dog and Pat Robertson, but being a Christian doesn't make you perfect or think you are. When you tell others that you're a Christian, you're saying, "I'm not perfect and that's why I need Jesus." When one tells others about their talks with God, they're not saying they're special and you're not, they're saying God has helped me through my prayers, and He will help you, too. Just try it.
As for Luster, he showed great courage to get a horrible man off the streets no matter where he was in this world. Luster's lucky he's in jail and not dead.