I understand to what point your getting at but even when the horse realizes the rider is not going to hurt them they still feel it.
Ok so your saying that it makes them go faster but you have a point but i do too, look at tis underneath:
Things that horses cant do to stay away from a whip:
They cant talk so they can't say stop using the whip on me because it hurts.
Secondly they are such magnificent animals they shouldn't be treated in such a way.
I know it makes them go faster but it causes them to slow down also. Some reasons:
The faster they go then the slower they go into the next race, if you put it this way, horses come along playing fine then comes only sometimes an evil rider wanting to whip the horse even more which always makes them a little scared with you.
So that is my argument about whips not too be used on horses.