I generally agree with your feelings about the lack of good in the player party but I do have to disagree with you here. I very firmly disagree that one can't turn away from past wrongs to be a "true" hero. You're right that the good done in the present doesn't cancel out the evil done in the past, but at the same time the evil done in the past doesn't cancel out good done in the present. I firmly believe that it's never too late to turn away from a dark path and do better, be better. You're not entitled to praise, acceptance or forgiveness for it, but if you're devoted to doing good and making the world a better place, then you can very much be a hero. Or at the very least, you can be a good guy.
And I'm not disagreeing with most of what you say here myself. A person who used to do bad things not doing those bad things anymore is certainly an improvement, and therefore a good thing. But as you yourself say here, that person is not entitled to praise or forgiveness, i.e., you don't get to be a hero. You stop being a bad guy, but you don't get transformed into a good guy. And as @william85 aptly points out, no matter how much good you do now, the people you killed don't ever get their lives back and the families of those killed don't ever get their loved ones back. Death is permanent, and therefore so is--and must be--the stain on your life for what you did.
