I'm a Brit who was taught to shoot at school (http://whitgift-ccf.co.uk/about.html), so I have a rather different perspective on this. I wouldn't describe it as fear or unfamiliarity, just a belief about risks and benefits. (One of those life experiences that seems weirder and weirder in retrospect; imagine Hogwarts with SA80s. The ammunition was tightly supervised, but unloaded weapons less so)

I'm not sure you could untangle the "mental health" aspect of mass shootings from the politics of it. Some of it is "extroverted suicide" but a lot looks to me like people have been radicalised.