The post-modern belief in relative morality is a significant part of the problem. As is the devaluing of human life.
The foundation of the problem is evil.
There has always been evil and there have always been evil people. When a society looses its will to proclaim moral absolutes and enforce them then this type of evil behavior gets more and more out of control.
The breakdown can be blamed on a bunch of factors but ultimately someone has to be responsible to teach and enforce ethics. If the parents are incapable, nothing in secular society is available to fill in. Even the church is walking away from calling evil evil.
Add the loose respect for life with the "glory & fame" our current media bestows on the perpetrators and this type of behavior is inevitable and will continue.