At some level, it doesn't matter if they are born or created (I think it is a combination, once again). But, they definitely exist. I would argue that the issue is for society to provide fewer opportunities for them to change from being trouble makers in the office place to being shooters in a Walmart.
I think of problems like this with set theory. Think of a big circle (with radius R) representing people who aren't shooters. There are people in the middle of the circle (at a radius of near zero) that will never become shooters. There are people right at the edge of the circle (radius = R-.0001), and it takes one of 20 possible factors for society to shrink the circle a micron, effectively placing them outside the circle. Society needs to work on all 20 factors. We shouldn't pretend that these are normal people (radius = R/2) who are suddenly deciding to move outside the circle.
Our leaders should not use one of the 20 factors in a cynical process to divide people at R/2 so that one group or another can retain power...without worrying what is happening at the edge of the circle.