(I&#x27;m strongly against gun ownership by private citizens. I struggle with questions like these but I&#x27;ll try.)<p>1) It&#x27;s mostly ignorance.  When we look at mass shooters we see histories of violence, or of drug and alcohol addiction, or sometimes mental illness.  The drug and alcohol addictions and previous history of violence are better predictors of future violent behaviours.<p>2) Reducing access to means and methods is an important part of suicide prevention.  People who complete suicide are more likely to have a mental health problem than the general population.  Reducing access to guns would help those people.  This does not need to be done through law. The taboo around suicide doesn&#x27;t seem to stop people doing it, but does it does stop people seeking help.  Ideally people would work together with their clinicians and carers to identify and ameliorate risk.<p>3) Some politicians seem to suggest that if you stop mentally ill people having guns you stop <i>all</i> mass shootings.  That&#x27;s clearly not true.  You stop some of them.  But when we talk about mental illness it&#x27;s not clear what those politicians means.  Do they mean serious, life long, psychotic style illness (rate about 2 people per 100)? Or the subset of that group who have command-hallucinations?  Or do they mean everyone who&#x27;s had a diagnosable mental illness? (Where diagnosable would be defined by DSM 5) - someone who was treated for depression two years ago? Someone with hoarding? Someone with OCD that was treated four years ago? It&#x27;s odd to see people who are pro-gun using this argument, because their calling for about 1 in four people to be prevented from gun ownership.  And not all mass-shooters use their own guns.  Harper-Mercer (killed 9 people) used a mix of guns owned by him and his family; Lanza used guns bought by his mother.<p>4) Looking at mass shooters we see sometimes see failed checks: people with histories of violence are allowed to buy guns; people are prevented from buying some guns (eg rifles) but allowed to buy others (eg shotguns). Wong&#x27;s background check took longer than 3 days, so he was allowed to buy a gun.  He went on to kill 13 people.<p><a href="http:&#x2F;&#x2F;www.nytimes.com&#x2F;interactive&#x2F;2015&#x2F;10&#x2F;03&#x2F;us&#x2F;how-mass-shooters-got-their-guns.html?_r=0" rel="nofollow">http:&#x2F;&#x2F;www.nytimes.com&#x2F;interactive&#x2F;2015&#x2F;10&#x2F;03&#x2F;us&#x2F;how-mass-sh...</a>