I ride without a helmet and essentially never go beyond about 12 MPH, and more often in the 6-8 range. I take sidewalks generously, stay out of mixed traffic, and frequently stay in low gear, and this is still over twice as fast as an average walking pace.
I think it's all relative to how much you're approaching it as "road cycling" vs "urban commuting". If you keep the seat high, lean forward, and pedal near your limits, you definitely need protection even if the road is empty. But if you're going at a pace and a posture that lets you stomp your foot down easily, the dangers come down to total loss of control(e.g. downhill, failing brakes) and unpredictable traffic.
The biggest danger with electric mobility going forward lies in blurring of the distinctions. When they're brought up to highway speeds, what you have is an underbuilt motorcycle with no safety features or licensing requirements.
