Most of the people who murder, rape, set shit on fire, blow shit up ... most of these, if not ALL, are strangers ...
Do you know the cartel dudes, in Mexico, that cut folks' heads off? - me neither bub ... total strangers.
I don't know anyone in ISIS, nor do I know a serial killer or a dentist personally ... once again ... STRANGERS!
So my point is very simple, you need to be concerned about strangers and the inherent risk they pose ... unless you want to get murdered and dumped some place in the woods.