There are a lot of reasons why people do the things they do. Mental illness, oppression, possesion, hurt, and anger and confusion are just a few.
Ultimately we are all responsible for our own actions, but our actions do not neccesarily define us. This is an interesting topic for me, because I am still trying to come to terms with my own life. If I was defined by poor choices I made, you would know me as a drug dealer. I would be defined as a thief, a whore and a drug addict.
I know now there were many reasons for the choices I made. I was molested as a child, hated by my father, raped as a teenager, and beaten as a wife. I was betrayed by everyone I ever loved, and survived my life instead of living it. I found ways to self medicated, ways to feel good about myself, and ways that I thought would make living a bit easier, until I could die, often wishing that just one of those bad choices would end my life. I don't even think they were concious choices... just an inevidable thing I did in my fog of existance. I was not living in reality and did everything I could to avoid it.
One could have argued that I was a horrible person. But I always had a good heart. Inside of me, deep where no one could ever see, I was vulnerable, I hated the way I was destroying myself, and I knew what I was doing was wrong. Even when I questioned God's existance, studied witchcraft, and played very dangerous games, that was not who I was at my core.
I know it is hard to see someone for who they are in spite of the things that they do, especially when they do horrible things to others. But no one is beyond the grace of God, and even though we do things because we believe it is right for whatever reason, we are never truly defined until we make a choice about our salvation.
Think of all the people that Saul had persecuted unto death before his journey on the road to Damascus. He was a cold hearted killer! And God transformed him, and GOD defined him - he was to be the Apostal Paul, a man of God and would lead many to salvation. He was not defined by his actions, but he was defined by God.
That gives me hope...