What are we capable of?

I was having a conversation with a friend of mine the other night. We were taking about her father and the unspeakable things he had done to her mom at some point. My response to her was that it was scary to think about these people being capable of terrible things - and how the wives or husbands of murderers and abusers never saw it coming. I said how it's scary to think you might marry someone - not knowing what they are capable of that kind of violence. She responded that she believed from her experiences that humans are all capable of everything given the right conditions. She believes that you or I could kill if we are put under the right conditions. I was shocked. I thought to myself "I'm not capable of that! Never!" Then I got to thinking about this and realizing that to a point she was right and I too had felt that way... It lead to me taking an unwanted visit to my past... Recently, I was talking to another friend of mine about not wanting kids and how I had never wanted them. She was asking me why I felt that way. I gave the answer "Because I have never wanted them". This was true... But I then had a flashback to the original moment these feelings became real. My life as a child was very different. My house was violent and dark. I remember feeling terrible and hiding in the closet trying to stay unnoticed. I remember blood, and bruises and screaming. I remembered the day I decided I wanted to take my own life... And It all came together. I am a rational, lucid, and reasonable person. I have a good heart and a world of happiness and positivity, but when put under the right conditions I wanted to take my own life. I remembered thinking that and looking at different family members who show evidence of mental illness and instability. I have watched these people break and do unspeakable things. My own grandfather took his life when my mother was just a baby. My mother and my sister both show signs of potential violence. Who is to say then that I don't have the same capability. I remembered this thought. I remember the moment of desperation when I decided that if there was even a speck of that inside of me I would do the world a favor and not have children. I couldn't live with myself if I ever inflicted that kind of pain on a child. I'm terrified of what kind of mistakes I could make if another life was entrusted to me. Could this break me too? I think I would rather not find out...