I remember reading similar stories about Buenos Aires...."don't go walking along Avenida 9 de Julio as you'll get mustard sprayed in your face and robbed even in daylight". " Under no circumstances stop and look at a map....you'll be jumped on and left for dead". Enough to make the nervous tourist cancel any plans they ever had of visiting the place. I find BA no different from any other large city in the world.....be careful and you'll be fine.
Truth is crime happens everywhere from Rio to Rothesay (that'll have you Googling) and if you believe everything you read you wouldn't venture further than the end of your road.
For every one unlucky tourist there will be many thousands more who only have happy tales to tell you about Rio I'm sure.