As far as I can see, if someone asks a supplier for a motor that will do 50mph, the fact that it is electric as opposed to petrol is inconsequential. They should be told that such a bike will have to registered, taxed, insured etc. The fact is that cycle parts are not really good enough for those sort of speeds. Brakes, tyres, steering head, shock absorbers, mudguards, lights will all have to comply with motor vehicle standards.
To fear that an idiot abusing the rules will bring problems down on all of us is not at all unreasonable or 'Moronic'
Just one horrible accident involving school children and a high speed, illegal electric bike could do it. Joe Public does not understand electric bikes as we all know and boy, does he love his prejudices.
Always remember the law of 'Unintended Consequences'