Gosh, y'all are making the US sound like a combination Wild West, war zone, and animal park where the visitors are the feed for the animals and entertainment for the natives. For all the bullshit and bravado, the US is acutally a very safe place to visit, and the danger of being robbed/assaulted/chewed up by the wildlife is fairly minimal. Take simple precautions like as previously mentioned - don't leave valuables sitting out in plain sight in cars (lock them in the trunk/boot). If you are not 100% sure of the neighborhood you're visiting, don't go alone and don't wander around like a slack-jawed idiot staring at everything new and strange to you. Don't lose track of your surroundings - when reading a map, don't unfold the whole thing and allow it to be a screen between you and what's going on in front of you. If you must consult your map in public, find somewhere to sit down and do it there. Looking like a gawking tourist, whether you're in Washington DC, New York, Barcelona or London will mark you as a tempting target for thieves and pickpockets. Check your map before you go, have a good idea where you're going, and be confident when you're there. Many (but not all) bad areas in US cities are pretty obvious. If boutiques and sit-down restaurants give way to take-out places with bullet-proof pass-throughs, liquor stores and pawn shops, it's time to turn around. Stick to main streets with lots of pedestrian traffic. Away from the big cities (DC, New York, Chicago, Atlanta, Boston, Philadelphia, San Francisco, and a few others) public transit is pretty limited. When you're in one of those places, though, if you stay near subway/light rail stations, you're generally fairly safe because if you get worried, you can always return to the station so long as it's open.
If you're heading out into the open spaces and think you might encounter wildlife, read up on the kinds of wildlife you're likely to encounter, and what you need to do to keep yourself safe from them and them safe from you. Most encounters with bears, coyotes, bison, alligators, etc that don't end well happened because the human was stupid and didn't pay attention to best practices. Announce your presence, keep a safe distance, and in bear country, don't keep food out in open containers - it attracts the bears and they can and will destroy just about anything between them and it, including your car.