Sorry, don't buy it. Having been a target of harassment through much of my school years, they caused me far more grief than anything my family threw at me.
The shooters at Colombine actually ran across kids they knew before the shootings and warned them to stay away from the campus. It sounds like the way they were treated at the school had a big impact on their behavior.
Many of the other kids who did shootings were outcasts or social misfits. In these cases, their *socialization* is what pushed them over the edge.
For the numbers of kids involved in school shootings at the public school level and the homeschool level, those misfit homeschoolers have a better track record. If being improperly socialized from being homeschooled were the issue or cause, then you could expect homoeschoolers to be far more disproportionately represented in going off the deep end and it's not happening. The facts do not bear that out.
Kids can be pretty ruthless (think Lord of the Flies) without proper adult supervision and that just is not feasible in the system as it exists today. It's simply a practical matter; not all the kids can be watched all the time, and they shouldn't be.
And that applies to this case how? Oh, right, it doesn't. Now if the family that these gang-bangers belonged to were not socioeconomically disadavantaged or if the kid had a parent who valued education enough to scrimp and save for a private education, then maybe they would have been saved from the influences in the community. So, I think my statement still stands.