Not to "muddy the waters" any more, but what are the group's thoughts on stopping your towed setup when needed? A trailer and dolly add more weight to what has to make it down the road, and ultimately what you have to stop. Granted, many vehicles cannot be flat towed from the factory, but quite a few of them can be towed with modifications such as a transmission lube pump. Many campers have that setup and are completely happy. 4-down is obviously the "lightest" way to have a toad.
Back to stopping, anyone towing a car needs to make sure you have adequate brakes on the towed setup, be it 4-down, a dolly, or a trailer. It is usually the law and it is certainly a question of safety. I tow 4-down and have an Even Brake setup. I have found through years of travelling like this that my stopping distance is not much different (if at all) from when I am not towing. 4 more tires grabbing the road when I need them to is great! I have looked at dollys and seen no brakes, electric brakes, and surge brakes. But only (if present) on two wheels obviously. I have seen many car haulers with tandem axles with brakes on only one axle. Add the weight of the trailer (or dolly) to the car being hauled, stopped by one axle's worth of brakes, and I bet I could stop in a shorter distance every time.
It is likely that many campers have no other choice than to do something other than tow 4-down. But please do your homework and make sure you can stop your setup as well as you can make it go. All "go" and no "whoa" is a recipe for disaster.