I have heard opinions that one reason for the large # of mass shootings is that there are no institutions trusted to act as a means to limit bad behaviors. Religion is not trusted by many. There is no institution to replace the way religion acts to curb bad behaviors, bad attitudes, and the ego-centric "me first" nature of many.
I see Mass Shootings NOT as the ONLY threat, but the "Tip of the Iceberg." There are other bad behaviors that do not get the attention from the Mass Media. Teen suicide, depression rates of teens, self-inflicted wounds ("cutting" oneself) are ALL UP and UP lots. There is a crises of a lack of values and morality. There is no respect (a significant decline, at least) of respect for: teachers, police, political leaders, doctors, ministers, and many institutions. To me, a key point is to not place trust in any one person or group of person, but in the values of love of Country, Love of God, and love of Family. I fear that there is certain, among many young people, even a lack of love OF SELF. That lack of Love of self means low self-esteem, that is often the reason teens and young people have issues of anger and anger management. Many young people (and older ones, too) lack the moral underpinning to deal with the set backs in life.
The 18 year old killer in Texas, did not even love his family, not really. AND HE first SHOT his GRANDMOTHER, before going to the school to shoot all those innocent children and kill two teachers, along with those 19 students. He was certainly a troubled young man, barely an adult (he turned 18 only DAYS before buying his gun(s) and ammo to kill his victims.
All the reforms in gun laws that have been proposed likely WOULD NOT have stopped this last mass killing. Background checks do not stop killers. They may SLOW them down, and may make them wait. That may save lives, but I am not sure that the delay is significant.
As I have said before, there are too many Guns (and Ammo) in the USA, too many crazies in the USA, and TOO MANY crazies with too many guns. And then there are the guns in the possession of criminals, who are not necessarily crazy, at least NOT to that extent.
There is also the theory that these mass KILLERS are PURE Evil Incarnate. If anything, these individuals who commit such crimes are weak-minded and lack a love of family and lack a moral grounding and foundation. Weakmindedness allows these persons to be influenced by evil folks. They will often use racism or anti-Semitism as a basis for their hate and to justify their anger and eventually their actions and evil deeds.
Bill Bennett, former Secretary of Education, tried to develop a sense of values and love for fellow humans outside of main stream religion. He did, of sorts, but LOST lots of credibility when it was determined that much of the profits from his book(s) espousing these New Morality values were gambled away in his person vice.
Controversies
Gambling
In 2003, it became publicly known that Bennett - who had spent years preaching about family values and personal responsibility - was a high-stakes gambler who lost millions of dollars in Las Vegas.[21] Criticism increased in the wake of Bennett's publication, The Book of Virtues, a compilation of moral stories about courage, responsibility, friendship and other examples of virtue. Joshua Green of the Washington Monthly said that Bennett failed to denounce gambling because of his own tendency to gamble. Also, Bennett and Empower America, the organization he co-founded and headed at the time, opposed an extension of casino gambling in the United States.[22]
Bennett said that his habit had not put himself or his family in any financial jeopardy. After Bennett's gambling problem became public, he said he did not believe his habit set a good example, that he had "done too much gambling" over the years, and his "gambling days are over". "We are financially solvent," his wife Elayne told USA Today. "All our bills are paid." She added that his gambling days are over. "He's never going again," she said.[23]
Several months later, Bennett qualified his position, saying "So, in this case, the excessive gambling is over." He explained "Since there will be people doing the micrometer on me, I just want to be clear: I do want to be able to bet the Buffalo Bills in the Super Bowl."[24]
https://en.wikipedia.org/wiki/William_Bennett
GOD BLESS AMERICA 
