You either think you need a supplemental braking system or you don't.
I suggest you read the following first.
Physics of Towed Vehicles
I think many folks that don't believe a supplemental brake system is necessary feel the safety aspect is overrated especially when cost of set up is concerned... tempered with the knowledge that they know their vehicle's towing ratings etc.
Though I don't agree with such thinking, there is logic behind it, and a good discussion about the need for supplemtal brakes can be found over at RV.net