I don't understand the "run-away" concern between towing four-down without brakes and typical towing on a dolly. If a car became disconnected from a dolly it could also be in neutral and have no brakes, hence could become the same type of missile. I trust safety chains are there in both cases to prevent a run-away.
That's not to say brakes are not a good idea for other reasons, like shorter stopping distances.
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