Drugs and mental illness, especially when combined, can create some very unnatural behavior in humans.
Having a history of working around criminals, many of whom were suffering from some sort of psychosis, has enlightened me to just what people are capable of doing to themselves and to others.
I could share stories that would make your blood curdle, some of them are just as bad or worse than the story in the news.
This isn't a new thing, like SR said, drugs have been a problem for millenia and bizarre behavior due to drugs and/or mental illness has been around for as long as humans have.
Yes, it is more prevalent now than it was 200 years ago, but it's not quite as common as the news would have us believe.
Unless your brothers are already involved in the lifestyle that would lead them to be in contact with people such as these, then they are at no greater risk than the other billions of normal people in the world.