If I’ve read it right you’re saying that if they are too slow to be riding a bike at a reasonable speed then they should get off it and walk on the correct side of the road for pedestrians ?.
If you really want to blow their minds try if they’ve got no lights at night they should ride on the pavement.Their usual answer to that is that they aren’t allowed to ride on the pavement.
There is generally a reason why people in good health and in the prime of their working life can’t afford to buy and run a car. 
