Costas mentality is that, generally speaking, that when people walk around packing guns that more bad than good will result. The gun culture he speaks of,I believe, is more directed at thug mentality. People who want to act like 'gangstas'. That a gun is the method of choice used to resolve arguments and disagreements in this subculture.
He offered no ideas of how exactly to curb this mentality or what new gun regulation would be enacted to prevent crime without taking away second amendment rights.