Why do they never blame the person that actually fired the weapon. it is 100% his/her fault. Not trumps fault, its not the guns fault, not video games/movies/parents, the world ...ect...
Blame the dumb ass deciding to shoot up the place.
Because people try to find a way to prevent the next one? So they are looking into common denominators. At which point they start thinking that storks bring babies, because there are so many of them around, in the months most babies are born.
(Example for a false statistical correlation.)
Then they resort to: "When I was young there were no mass shootings, so what has changed? Videogames." Logic, because they are old.
The issue here is, that in the past lets say 40 years quite a few things have changed. One of them being that people can publish their mass shooting videos, and manifestos on the web, for any brittle mind to pick up and obsess about - so this finally adds the aspect all mass shooters crave - posthumous glory and recognition. Be it even only with a very select group on the internet (the 8chan crowd + company). And a few other things as well - like online bullying, faking empathy on social media, social worth by number of friends society, faster rate of perceived social change. US Presidents spreading hate propaganda to win elections. Parents having to work more than in the past generation to sustain the same income level (family social structures change).
But people love single issue theories.
And they don't understand - that blaming something on a thing that the vast majority of people now do as a mode of recreation (play videogames), doesnt help to tackle the issue at all.
I mean there is an even more obvious correlation, social media is proven to negatively affect mental health in quite a few ways - but old folks like getting images of their grandchildren (for which they strangely need an ad company moderating the exchange), and politicians love it for ad campaigns, so nobody is picking that up.
This is not a sufficient explanation as to why this is now a more widespread issue - but rather an example that teaches you about the validity of single issue theories in complex worlds.
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edit:
Videogames are used by the military in desensitization training. So to have human material lose 'the fear of pulling the trigger', and be able to act as instructed under stress situations. So there is that causality. That always was there. You could argue that this is enough to ban videogames. But then you have to accept that your society isnt realy working - because people can be influenced so quickly in your minds - that working social structures, or education wouldnt be worth anything, because people are just too damn emotionally guided.
The studies about videogames increasing violent behavior dont hold up. Activasion only rises temporarily. Thats a seperate thing people tried to prove.
There is also an 'issue' with people using media as a backdrop for their fantasies. If yours are violent - and you have COD at hand, guess what - best tool for the job. Keeps you engaged in your violent fantasies for hours. But then - thats an issue with all media.
Are videogames more 'effective' at it (emotionally stipulating) probably.
So the point could be made, that videogames transform more 'susceptible' beings to mass shooters more effectively.
The issue here is, that you cant test that. The sample group is too small.
If you then point at other countries, and low mass shooting numbers, compaired to the US - this points at gun culture also being involved. There is no other 1st world country that propagates the "heroes can have weapons/problems are solved with guns" myth quite like the US. So if thats something you believe in. And you hate society. And you have violent tendencies. And you like shooters. Which might very well have desensitized you to the conceptual idea of shooting crowds. And your parents dont care. And your school is talking all about inclusivity, but never really meaning it. And your president is putting the fear of god into people over migrants. And you have access to weapons and ammunition in every super market. And you think that people will read your manifesto and "change their wrong behavior". Guess what.
