150 years ago we began as a culture, to entertain the idea that man did not have a distinct ontological purpose and no higher destiny then to be reabsorbed back into the biological mass from which he originally sprang. In such a case, any sense of destiny, purpose, nobility, not to mention eternity, all became pipe-dreams. We were, at the core of our beings, merely some insignificant part of an ecosystem that was by purely materialistic or naturalistic forces, being blindly guided by the impulse of pure chance and utter meaninglessness.
In the course of time we embraced these concepts into the American system of education - a system already tilting toward the left by pragmatist ideologue leaders such as John Dewey - a stepchild of the Hegelian philosophy of the dialectic deeply espoused also by Karl Marx. In the school system we began to teach our children that they had no ultimate destiny and that they were merely part of the cosmic and biological accident that occurred with no meaning, no hope, no reason, no future.
This mindset of course had very predictable effects on the generations that followed until through weakness and abdication of the church on the one hand, and an opportunistic charge by the progressive culture on the other, a fatal, but not unexpected court-decision was made in 1973 legalizing the wanton slaughter of untold millions of lives in what has become a modern-day holocaust. Since then, some 55 million humans each with a unique DNA profile, have been erased as if they were nothing more than unwanted debris. Once again, we boldly and loudly made the statement that life was not created in the image of God, in fact life had no meaning at all, really.
Following suit in the cheapening of life were then both the major motion picture and the computer gaming industries with their relentless parade of blood, death and mayhem with no consequences. Add to this the ubiquitous proliferation of psychotropic drugs over the last ten to twenty years. On March 22, 2004 the FDA published a Public Health Advisory that reiterates several of these side effects and states (in part) "Anxiety, agitation, panic attacks, insomnia, irritability, hostility, impulsivity, akathisia (severe restlessness), hypomania, and mania have been reported in adult and pediatric patients being treated with antidepressants for major depressive disorder as well as for other indications, both psychiatric and non-psychiatric."* it is estimated that one in ten people in America are now prescribed SSRIs.
Recall that these drugs are being prescribed to a population who are already disenfranchised from God, who have already been raised in a school system and culture where the life of man is meaningless, who live where babies are wantonly slaughtered just days, weeks or months before they would somehow cross onto that magical realm from unviability to viability.
Then such subjects of this culture of death are handed a gaming device where they can carry out yet more fantasy of mayhem and gore. Now obviously not every child of the gaming culture is a potential mass-murderer, but out of these generations, raised in an atheistic, drug-infested culture there are liable to be those who through some other form of mental instability, cross that line from fantasy to reality, acting out in their own world the dark, psychotic play that has been the ceaseless inner horror movie playing deep within for perhaps years.
That's why we can expect yet another Sandy Hook style shooter in the near future. The odds are against us. Tragically, It is not a matter of "if", but "when."
So in summary, it is not the case that you can point to one phenomenon like the Beatles and Rock 'n Roll in the 60s, the Vietnam War, the hippie culture, the removal of prayer from school etc. etc. as the case for our cultural decline. Rather, these are all symptoms of what really shifted when we began to declare that man was not made in the image of God, a declaration not in fact made as a result of empirical data or proof, but rather as the result of a theory still unproven - a theory which produced an onslaught. By means of the mechanism of the dialectic, what Darwin was doing in biology, Marx was doing with economics. In this, both Atheism and Progressivism have joined forces and are now pouring gasoline on the culture of death in our country. Of course, their knee-jerk reaction is to seize the guns. If they succeed in this, then they have closed the coffin on this chapter of our nation's very existence.
The only obvious answer to this dark reality is for the church of Jesus Christ to finally awaken to both her true identity and her true task.
Because it will not be "if", but "when"
* citing from http://ssristories.com/