Does violence define masculinity?
First, he claims that men = violence is entirely cultural... that it's trained into boys from their youngest years. Part of that is true, but it's also not true. We know that higher testosterone is associated with higher aggression in both men and women and men tend to have more testosterone. Violence is actually essentially human. We don't train it into ourselves, we train it OUT.*
This isn't to say, at all, that our cultural fascination with criminal violence is good, or that any of the examples that the NRA commentator lists are wrong. But he (and others who make similar arguments) fail to understand the source of the fascination. Our caveperson genes admire strength because strength means meat on the table, protection from sabertoothed tigers, and warmth through the winter months. Because the mirror side of criminal violence is the capability to provide protective violence.
Our society has been spending a great deal of time and effort trying to convince men that they shouldn't be protective. We're not talking hulking muscles and bloody swords here, we're talking opening doors. Little things that put men in a role of looking out for others. Showing you want that role by offering to carry her books home from school. "How dare you suggest I need looking after?" But looking after others defines masculinity as much as nurturing defines femininity, and while physical strength is attractive, the role doesn't require it. Dweebs in vacation duds and deck shoes set the women and children in the lifeboats first.
Take that away. Take away the quiet protection, the provision, the admiration and thanks for carrying my books or opening doors. Vilify outright the young man who beats up bullies or protects the weak. Mock the adult man who feels important with his conceal carry pistol because he thinks he might be able to stop something bad happening someday.
Do all that and all that is left to satisfy our primal biological imperatives and signal which man is the most masculine is criminal violence.
*(And thus the true social tragedy of denying the reality of Original Sin... that we are born sinful because we are born human becomes this odd notion that we don't really have to fight our human nature because our human nature is just fine, thankyou. Unfortunately, reality is that humans didn't "claw our way to the top of the food chain" or become apex predators by weaving daisy chains.)