Why is the world so much more VIOLENT now than it was decades ago when I was a kid? More guns? More hate? More corruption? WHY?

Lots more people.  

The world has always been a violent and hate filled place. The difference is in the more widespread acceptance of corruption. For a human shortcoming to become more prevalent, it usually must be more accepted, excused, with a blind eye turned to it. These things are byproducts of spiritual and moral decay. All of that silliness that we did in school in the name of a nuclear attack response was just government propaganda to make us all believe there was something we could do to give us a chance at survival. 

You don't remember church attacks like the one by white supremacists on the 16th Street Baptist Church in Birmingham, AL, in 1963 that killed four young black girls? Wow.

It's not.  Just the means have changed

With the advancements of media we hear about more things than we used to.  We have access to news in the palm of our hands (smartphones).  No more waiting for "news at 11'", now it's live. 
There have always been evil people whose main goal is to hurt or destroy other people.  For some twisted reason, people seem to enjoy hearing/watching atrocities.  We'll slow down and rubberneck at traffic accidents hoping to see a body or come other carnage.  Our most watched TV programs are about people killing other people.  When some sicko shoots up a school we follow it for days.  The media squeezes out every little detail they can about the "suspect".  What better way for other whacklos to get attention than to be on national TV!  Shoot up a school and you'll get national attention.  Bomb a church and you'll get national attention.  Commit hate crimes and you'll get national attention (they'll even show your hate graffiti - blurred, yes, but still quite legible).  Want instant attention?  Stream your atrocities live on social media so all the world can watch as you commit it.

When we hear of another school shooting, what's our response?  Is it exactly the same response we had the first time we heard of a school shooting?  Or are we a bit more numb to it.  Almost as if it's inevitable.   "We had 3  school shootings in just one week.  Why, I remember when we only had 2 in an entire year".   I'm not saying they aren't tragic, but that we're getting used to them.  Instead of taking care of the problem we just accept it as "how bad the world is".

Furthermore, we don't take care of the problem.  That might interfere with someone's "rights".   Murders have rights.  Criminals have rights.  Rapists have rights.  Why, I bet even guns have rights!   If someone is guilty of shooting up school kids, they not only forfeited all their rights, but their life as well (regardless of their age).  Let other sickos know that if they do the same they will receive the same punishment.  Not life in prison.  Not some lawyer saying they're insane.  Justice.  

Terrible things happened in the past, child abuse was covered up, (still is to some extent) and domestic violence was ignored.. but, but, but.. I do agree people seem more cruel now, more callous and I do see this every day..

Little things like, when driving, there are rules and etiquette such as when it's your right of way, the other person waits.. people seem not to be doing that anymore and I think this all ties into a kind of selfishness and lack of compassion that allows people to treat others as if they don't matter.. only what they want matters.. 

There's some support for this argument as they are finding that among the young they are considering actually teaching them compassion and empathy as some seem to be growing up without these qualities  

There are a few factors which I think are important.  Among them are, first of all, the concept of time.  Which has been unnaturally skewed by our dependence upon entertainment media.  Which wraps up and settles whatever it brings up in a matter of hours or sometimes even minutes.  So when people want what they want - now they want it NOW.  Immediately.  Not willing to wait and work and hope and pray and sacrifice and learn and get to know how to handle people and  become the masters of their own fate.  All of which naturally make us powerful as individuals we can respect ourselves and we feel we have control over enough of our lives. So lacking these things which take time and effort to acquire and still desiring power they seek it by means of a gun.  Which equals the power over another life.  Just get a gun and threaten others to get what they want or blow people away if they do not cooperate in giving them what they want.  As you would say - "easy peasy". 

The more people lose religious faith the less reason they have to respect one another.  Until they come to see themselves as "god" and come to think only in terms of themselves as the center and purpose of the universe.  So if course if they see that as true then anything they do justifies , any means,  justifies them because they have set themselves up as the only authority. 

Another aspect is that many people love and are attracted to violence.  If that were not true then there would not be a paying audience for so many violent motion pictures and DVDs and Blu-rays.  It makes their lives interesting and worth living. So TV networks and newspapers pander to this interest by giving them ever more and more coverage of violence - often as it happens.  So they become inured to its baleful effects and just accept it as normal, inevitable, and , sometimes, useful. 

So people can get the kicks and stimulation they want  from the violence and then feel they are compassionate by mourning and despairing over the victims of violence.  All of which gives them a chance to feel ways they want to feel vicariously even if they don't participate directly in the violence they are deriving things for themselves from it.