Ignoring the inclusion of people up to age 24 as "youth", I was struck by this line:
The majority of surveyed youths believed that "revenge was a good thing" and it was "OK to hurt people if they hurt you first."
That, right there, is the problem and why we have "gun violence" in America.
It's not because people can own an AR-15, 30 round magazines, blah blah blah ZOMG Eleventy!
It is because there are people who think that inflicting violence on another is acceptable means for resolving dispute.
I know a lot of gun people. My local range is a Conservation Club, and membership is pretty robust, for a semi-rural area of East Central Indiana. Turnout at the weekly trap shooting contests is good. Finding other shooters isn't hard to do. And yet to a person, we all abhor the idea of shooting another person. It's always the same refrain over and over again: "Every day, I pray to God/Buddah/Shiva/Earth Spirit of Life/Flying Spaghetti Monster that I don't find myself in a position where I have to shoot someone."
Then there are the folks mentioned in that story above... those who have such a lack of respect for another's life that they feel it's OK to enact violence as recompense for a perceived slight.
If you want to end "gun violence" in America, or violence in general, you need to change that mindset. You need to fix THAT problem, not limit magazine capacity to 20 (or 10 or 7) rounds. You don't fix the problem by banning "assault weapons of war" or shoulder things that go up. You have to change the way bad people think.
But that's hard. That will take work and time, and a goodly measure of both. And inherent in that method is the statistical probability that someone will slip through the cracks.
But if you want to fix it, that's what you have to do.