Actually, yes. One real life example - colonoscopies. There is no medical requirement that people be sedated into twilight for colonoscopies (and very rarely people do get colonoscopies without sedation), but most GI doctors require sedation because it makes the process much easier and quicker for the doctor, and much more pleasant for the patient. Twilight sedation (and the risks that accompany it) is not necessary for the procedure, but it makes for a much better patient experience, and so many doctors will not proceed without it. Is that ethically cavalier? To condition a necessary and potentially life saving procedure on the patient’s willingness to be sedated, even though the sedation isn’t required?
And of course there are also many parents who will give their small children benadryl before a long flight, to make life easier on everyone. (that is controversial too)
[and yes, there are distinctions between colonoscopies and horse shows, with one arguably being much more necessary than the other.]
Now part of your point is that as adults we make the decisions for ourselves (including skipping the colonoscopy if we don’t want to be sedated), while children and animals have the decision made for them. And yes, that means that extra care needs to be taken when choosing what actions to take, to ensure those choices are in the best interest of the child or animal.
A nervous horse having a meltdown when 3 months of stall rest are needed is also NOT consenting at all. Do you see sedation in that scenario as ethically gray?
Again, I don’t see using Ace at a horse show as the standard, and I definitely do not support it being used if it is not allowed. When it is used, it should be used in a legal way, and no more than absolutely needed. But I do think there is a time and a place where it may help. Just as it would be lovely if all horses went happily in D ring snaffles, but some do need more than that.