While most here might agree that we have issues in our culture with parenting, we are talking about a mentally ill individual. There is always the possibility, and even the likelihood, that no amount of good parenting is going to help when you are dealing with a deranged person.
As far as "sites like this" always talking about causes and cures relating to firearms, this is a gun forum not a parenting forum. There are other venues to talk about those issues, and just because we are members here and talking about gun issues here doesn't mean we aren't dealing with the other issues in our own way (my wife and I have been teaching parenting classes through our church on and off for 12 years).
Yes, you are right. It is a factor. Some just might prefer to keep the non gun-related issues to their proper forum and context.