That's true, jd. we are all road-users.  And there, I think you have made the point.

 Cyclists go along the road, propelled only by their natural legs. 

Whereas car-drivers are artificially propelled, by a powerful internal-combustion engine. This engine can make the car go much faster than a bicycle.  So a car is more dangerous than a bicycle.  And so should be licensed.

That's very clear, thanks!

As for horses, they seem to eat too much food  to represent a economical alternative to the bicycle.