First, let me preface this with the fact that I grew up during Ted Bundy's crimes and with a parent who read a lot about true crime.
It's not the guy with the salvage van you have to worry about - you're not going to get in a van with him, so no risk. The danger is with the person who appears "normal", who fits in and doesn't raise red flags. That nice looking guy at the university with the broken arm who's struggling to get his tire changed...
People who would do you harm aren't always the weird ones.
As for camping, I think it depends on where you go:
Traditional campgrounds - not really much risk. They are usually fairly remote and, contrary to Hollywood, psychos don't wait 9+ months in a forest waiting for YOU to show up to kill. Campgrounds closer to towns are more likely to have issues due to the "weekend party" crowds, but if you keep your distance and don't confront them, they won't be more than a nuisance.
RV Parks - not really much risk. They are usually closer to a town, but cater to older couples with some families. You're not likely to get meth heads, etc., shelling out $30+ per night to stay there. They tend to have more rules and regulations that keep "rabble rousers" away.
Trailer parks - more risk. Much more varied residents. Long term and short term. Located in low rent areas. If you stay in these places, it is really best to check it out during the day and at night before committing.
Boondocking - can go both ways. Depending on where you choose to boondock, you can face more or less risk. That risk may not be with people, but with getting stranded.
Overnighting - higher risk. Walmarts, truck stops, etc. Depending on the neighborhood, store clientele, etc., you may see more problems here than elsewhere, but for most people, there are very few issues.
Stealth camping - higher risk. Parking in neighborhoods, etc. The risks here are from getting noticed by residents or that someone will try to break in thinking it's an empty RV.
Reality is that when you're traveling, you're much more observant of what's going on around you. That lessens the chances of something happening. Bad things are more likely to happen in your home town because you run on auto-pilot a lot of the time and miss signs of danger.
