Parents telling me I ruined my son by making him fatherless

My son is 15 and is on probation because he keeps getting in trouble. He's on a first name basis with at least 3 different cops and has already spent two weeks in juvenile hall. I've been talking to my parents about him because he stresses me out and they blame me saying I shouldn't have taken his father from me and boys need a father. When my son was 4 and he was with his dad I came home early and walked in with my 4 year old naked and my ex husband touching and doing things. I called the police and he plead guilty and went to prison. My son doesn't remember which is a good thing and I don't talk about it so he can live an untraumatized life. My parents kept telling me I should have let his dad have supervised visits and that most prisoners come from single mother homes. That my son is already a criminal and that it's not too late. His dad out of prison now but he does not remember his dad. They keep saying just have super visits so his dad can get him straight and kids need their parents no matter how bad they are. I'm confident in my decision to keep my ex away but my parents are saying because of that it's my fault that my son is a delinquent....