I agree that mental illness can be a factor, but it's also pretty clear that the pressures of a dominance-based social system are as well. There's a very clear desire to "succeed" in patriarchal hierarchies - often as a result of having been abused by them in the past. Rodger was bullied by other boys. So, part of the solution, is, I think to address the ways that such hierarchies are normalized and seen as just a part of how things work - when in many cultures that isn't how things are at all.
As I said in my piece that was more generally about the entire manosphere, intentional radicalization is taking place there - with way too little government concern for it the way other sorts of terrorists groups are monitored. Violent hatred and disdain of women is so run of the mill, that only in the instances where it has lead to mass murder or clearly overlaps with things like racism does anyone take it seriously. That needs to change as well and in some cases, it is, but more is needed.
Apparently, there is a UK based group called CALM that is doing great work offering support to young men in schools, clubs, pubs, prisons, etc. I want to find out more about them and perhaps write something up. It's "infiltrating" cultural spaces with an aim to provide a positive and constructive message and to give an alternate "community" to those who might end up in the manosphere. I think we need a lot more groups like that as well.