The main problem you have here is that the assumption that "every mass killing" is as you describe. Only the ones reported on the news fit that bill and are only 15% of the mass killings in the United States. Mass killings in downtown Chicago, for example, where gang members shoot up a house full of people are not reported in national news, and nobody seems to care. (It is my belief that nobody cares because there are already draconian laws against guns there). In a place where literally thousands are killed in a year, sometimes into 3 digits in a weekend it simply is ignored by the national media. You should try to figure out why those mass killings are the ones are "missing" from your knowledge rather than pretend that only the ones that you hear about should be the ones we are talking about.
You don't have that excuse, I don't believe folks with a JD (Juris Doctor, it's what lawyers get when they graduate it's like an MD, but for law and equivalent to a Masters Degree in actuality) should be forgiven for deliberately ignoring crimes and pretending that "all mass killings" fit within a specific narrative presented in the national media. You don't get a pass, you are driving this specific narrative on purpose and without regard to the truth. No matter how many times I read your hacktacularly partisan nonsense it never fails to disappoint me. I keep expecting you to be better than that, but you just aren't.