One thing is certain, any website that SELLS braking systems will post the requirements for TRAILERS, which is not the same as a "vehicle in tow". The map above shows that a braking system is required in Florida when it is not required for a VEHICLE towed behind a motor home. As Executive mentioned, most states require that you must be able to stop within a certain distance but I found no state that specifically required a braking system for a toad.
As far as being sued if you don't have a braking system and get in to an accident, the sky is not falling.
I have a braking system for my toad and use it but if it breaks, I am going to continue on to my trip, no matter where I am, with the piece of mind that I am not breaking any laws no matter what state I am in.