I'm not even very interested in "how." And I am certainly not interested in the various pundits emoting over how "guns kill more people than terrorism," which is patent nonsense; it's like saying "Cars kill more people than running:" one is a thing, the other an activity, and guess what? $ACTIVITY often involves use of or interaction with $THING. You cannot extract meaningful numbers from that.
Nor do raw numbers tell the story. We have a very large population as countries go, and if you use raw numbers to compare anything that is an activity done by people, you're going to find the United States, India and China near the top of the list. Per capita, the United States does not have the most mass shootings; this country is number six. Still nothing to be proud of -- but we also have way more guns per person than Norway, Finland, Slovakia, Israel and Switzerland. (Perhaps we're better, saner people than they are?)
And will someone please explain to me why it is a half-dozen people -- who just happen to have skin darker than a paper bag -- can be killed in Chicago (etc.) by person(s) who are also dark-skinned, and it's treated by the media as pretty much routine -- but when victims are pale and/or when killers are pale or cops, suddenly it's a much bigger deal and rates national attention? (The murdered TV reporter and photographer in Virginia apparently count as a "mass shooting" now, but if it's four dead African-American punk kids on the South Side? Nope.)
In the present mess in California -- California, with the highest Brady antigun rating of any state! -- the ijit news media still wavers between "workplace violence," $GENERIC_MASS_SHOOTING and -- flinchingly -- Not-So-Sudden Jihadi Syndrome. Gosh, remind me, would you, just what organization it was that promised large-scale violence here in the U.S. in the wake of the attacks in Paris? ...Not Black Lives Matter protesters, not the NRA, no, it was... C'mon, one of you has the answer, NBC? CBS? CNN? New York Times? Do any of you know who....? --Thought not.
Nope, it's All Gun Control, All The Time in the national news media. President Obama promised to do all he could to push for more gun control and look, what a co-incidence, he's got himself mass shooting after mass shooting (no matter how much each one must be tortured to fit the mold) and he wants Strict New Laws to restrict the law-abiding. 'Cos you know, fiftyish midwestern spinsters who own guns are exactly the problem, and must be stopped. Or, realistically, more likely to comply.
Yeah, that? Don't count on it.
1 week ago