I think we all know that - which is why groups like the FEI have rules in place to protect horses from people having temper tantrums and taking it out on their horses - its also about doing everything they can to not bring their sport into disrepute - sure its not always working the way it should and the rules do need looking at to be careful they're able to be interpreted properly but without any rules it would be a downhill slideThere are a lot of things in life that shouldn't happen. But they do. There is no 'magic age' where everybody is suddenly a rational adult. Just look at the world around you. In a perfect world there would be.
I don't think there's any court of law situation where someone can put in a plea of 'well I just lost my temper' and get away with a crime
I would think that using pain meds - for one example of drugs
To mask an injury that needs time and rest to heal so someone can continue riding/working a horse is abuse
To help a horse stay active when that's better for the horse's well being is not abuse - though with something like wear and tear arthritis you still have to weigh up beneficial exercise against the sort of exercise that could aggravate and accelerate the condition