Rio is indeed dangerous, and when we stopped there for four days we were told "don't use the subways" - some of the worst offenders were children, and "ladies of the evening". Both would pickpocket you.
The children would swarm on you like bees and have their hands in every pocket you have within seconds, then disappear to another car and off at the next stop.
The women would come up and pretend to firt with you by touching where your pockets are looking for your wallet.
In Venezuela, many ships offered shorex to Caraccas. I was on a tour while working for HAL, and the guide (knowing I was staff) told me to stay in the back of the line and watch out for pickpockets. Throughout Europe, especially southern (barcelona, and Italy) there are Gypsies who wilpickpocket you.
The worst for violence is northern Brazil - Santos, Salvador and Recife. There you can get mugged or worse. Never walk alone carrying a backpack, purse or camera bag. I have friends who have been mugged there and even heard of stabbings of cruise passengers there.
I was there in 1983 and was carrying a huge camera bag. I sensed i was being followed by a young man, and promptly picked up my speed and got to the center of town as quickly as i could.