We're only quasi-anonymous online. Could knock on people's doors with very little effort and no illegal hacking whatsoever. We volunteer so much information, much of it seemingly innocuous, than anyone reasonably intelligent can piece it together and come up with a general idea where people are, and with a willingness to find out specificly, do so.
As to trolls, would say they represent only the emotionally stunted immature users of the internet who have no other outlet for their frustrations. Too with drawn or socially inept, they vent their dissatisfaction online because they know what would happen if they did it in person.