I'm probably going to throw myself into a topic that I potentially will get chewed out in, but to me, I personally want to believe that humans are innately good. Since this conversation seems to have driven towards more about defining the difference between good and evil (which to me seems to already be established), I chose to get right back to the question in hand. ^^;
Deep down, everyone has imperfections. But despite these flaws, mankind has proven to have small fragments of hope and morality inside of them, regardless of who they are. Even those who commit crimes or have severe flaws in their character have small glimpses of another side of them that I refuse to ignore.
A gang-member can still have a softer side and sense of loyalty towards his family (related by blood or group), often going to extreme lengths to either serve or protect them, while holding a sense of moral code to keep them by their side (and likewise, be protected by them in return). A drug-user/trafficker can still have amazing talents and an incredible sense of compassion and kindness towards others, with the ability to inspire and enlighten others in a (non-physiological) sense by what they say and what they believe in. I've even met alcoholics who were incredibly honest and organized, and had a duty to work hard and love their families unconditionally, even if their addiction had to be rectified.
Everyone has the potential to swing one way or the other, but I want to believe that people are good. Pure, unfiltered evil seems so rare and promoted in fiction nowadays that I can barely believe in it. Yes, the real world is harsh, but even then, I've seen small sparks inside those I had prejudice against that I feel ashamed to have claimed they were downright bad to the bone.
I guess what I'm saying is; it's really easy to see a bowl of clear, purified water darkened by a drop of black ink. But no one ever realizes how much of a bowl of ink is actually water until they take the time to filter out the two.
(Sorry for interrupting. Please feel free to argue at each other about definitions. *glances at BS/Gl1tch/everyone else* >_>)