If you think random acts of violence are more common now than in the past you are correct.
Violence has often been a part of the human society, wars over territory and such have been a concern for thousands of years, but actual random acts of violence are a relatively new thing.
In studies done on rats and mice, John B. Calhoun noted that as the populations grew so too did the occurrence of random acts of violence. He provided the animals with ample food and water, so he could eliminate "need" from the cause of violent outbreaks. What he noted was that as populations grew the compassion the animals had for one and other shrunk. They no longer acted the same towards one and other, even simple parenting skills declined.
The rats, or mice, were in near constant contact with each other and this caused them to devalue others of their kind more and more over time, leading to the increase in random acts of violence.
In the past when people lived rurally or in smaller communities (and in areas where these smaller communities still exist) people still greet each other with a "hello" and they still make eye-contact, even with people they do not know. In big cities people mentally distance themselves from others, they do not say "hi" to people they walk by on the street and avoid eye-contact.
We have already reached a point where random acts of violence are occurring, and are at a place where they seem to be quite common.
As parents we must raise our children to be compassionate to others, but equally so if we have lots of children we need to take responsibility for the fact that we are just adding more of a burden to the problem.
More people = more stress.