I’ve competed in lots of different horse sports and usually carry a crop, honestly more from habit than anything, but in my experience, you would get booted from most competitions if you repeatedly hit your horse with the stick, period, let alone full force like jockeys often do. I remember one time at a h/j show there was a girl in the warm up arena that was really mad at her horse for refusing, and furiously whacked it a bunch of times, and the ring steward asked her to leave.
I never really thought about whip use in racing very much until recent years when others have started talking about it. The more I think about it, I think its the right thing to do. The horses down the stretch are generally giving all they have- how many times have we all seen horses under the whip break down? Not to say that it would have prevented it but maybe in some cases.
The best race I ever saw in person was Rachel Alexandra’s Woodward- I get chills just thinking about it, but wow she was really beaten excessively too down the stretch.