Utilitas - your comment doesn't enlighten or advance. It seeks to place a blame on one segment when it applies to all.  Your single issue focus blinds you.  I presume you are referring to the abortion issue when you say progressives hold life in little value.  As a proud progressive (I prefer "liberal" as it implies "freedom") I value all life, even the lives of those I consider my adversaries.  It would be just as true to assert that the non-progressives foster a culture of  free-market competition which values profit over life (after birth).
But that sort of assertion doesn't get at the question of gun violence - which was the point of the article.