This is a very interesting topic and one worth discussing.
As I teach my children, you don't need to be paranoid in life, but it is wise to be cautious, think ahead and be prepared. If you own any type of insurance policy, you are already somewhat practicing such a mentality - although in some cases, you're simply adhering to what's required by law. You are also acknowledging that bad things can happen without warning. I always chuckle when thinking about our life insurance, because we're betting we're going to die and the insurance company is betting we're going to live.
I love having fun and being adventurous, but try to minimize unnecessary risk. For example, I've been an avid cyclist since I was a kid, but NEVER ride without a helmet. Yes, it's been put to use a few times, though some would say it doesn't seem to have prevented damage to my brain. :)
Anyway, the same thought applies to the decision about placing a person inside a camper (especially one not equipped with any safety devices, such as seat belts) when on the road. Between point A and B, my kids can do almost all the same things while belted inside the truck that they could do inside the camper. The huge difference is the amount of effort engineers put into keeping occupants safe inside a motor vehicle. True, there is still risk, but in the event of a high speed collision, I believe the occupants stand a far better chance of walking away without an injury when inside my truck, than riding inside the camper. In other words, riding in the camper is an unnecessary risk, that doesn't significantly add to ones enjoyment, but does expose the passengers to the threat of life altering injuries,or death, if involved in an accident.
NOTE: My statement is assuming there are enough seats for each passenger (as in our case).
After reading through this thread, some may come away with a different perspective that could potentially save a loved ones life, or prevent significant injuries. For others, they may not view riding in the camper as an excessive risk. We each have choices to make, but should also realize, the safety of passengers under age 18 is truly the adults responsibility.