I think the motto should be, and is, with AND, "ever mindful."
This consideration you challenge us with is one I hope we all continue to ask ourselves and each other.
Mentioning the vulnerability of the younger horse brings to mind that there are a great many horses that show no sign of haven't broken down in the back after many many years of fairly heavy use.
A recent example, a 37 year old record setting (for total miles) endurance horse, who, as you describe some horses, seems eager and willing to saddle up and hit the trail.
I offer this as solace.
Many of our associations have the potential to do harm. Take having children, for an example.
Owning a dog, cat, bird.
Just having a significant other.
We can find a great many examples of harm being done in those circumstance.
Yet we chose to do them.
Because of the potential payoff for both parties.
What does a horse get from associating with us?
Many, if we turned them all loose, would simply starve or be eaten.
We have bred them away from their wild abilities. We in the U.S. have a long history of turning horses loose, or simply having them go missing. We assume they survived in the wild, because some did. But how many didn't?
If we are going to keep them as companions we owe them more than just feed and shelter. We also owe them our companionship and a relationship that is interesting and rewarding.
Horses are constant learners. They are curious and playful, for the most part, if they have the chance.
I wasn't attracted to AND because I saw more effective ways to dominate a horse and get him to do more interesting and spectacular behaviors.
But I was by the possibility, the potential, to be with him in ways that were spectacular and interesting for HIM.
Look at what AND horses are doing. Without spurs, whips, threats, or dominance. Just with companionship and play.
Riding can be more play.
Years ago (about 1960 or 61) doing a great deal of training of horses, I developed a way of removing pressure, suddenly and dramatically.
I got off the horse as a matter of training protocol.
And I did it frequently. I coupled it, because I was a trainer, with reinforcing desired behavior, and it most certainly was, typical of the times in the horseworld, straight up "pressure release" method.
I did it because I saw it as a logical next step. But it, and the work I did preceding it as I developed as a trainer pointed me down what I thought was a dead end path.
I know now that the eagerness and energy I could get horses to put into their work, their performance, was in response to my showing them I could play. I could get off, walk about, talk with them, let them examine things.
Thus they linked riding with my getting off. How clever I thought I was. But I missed something very important. I had passed over a threshold, one it would not cross again for nearly 40 years.
The horse began to train me.
I came to care more about the horse, and some specific ones, than I cared about their performance.
I could not shake that, and I knew my professional life as a horseman was pretty much over. My very last job was mostly hanging out with a band of broodmares, looking after them, caring for the two stallions in the program, and one more special thing that put finished my career.
I had a 4 year old QH stallion I'd taken in trade. And he became my mentor.
I reached a point where I stopped performance outcome based work with him entirely. I stopped riding him. We played, and we chased each other like wild horses. In the paddock and in the pastures.
I had a lot of regrets at the time. I knew I was a rising person in the horseworld. I was learning, before those many long quiet months just hanging out with Koko, to get performances from horses that were out at the cutting edge.
But there was nowhere for ME to go personally. Not morally, not ethically, with the horse.
The last horse I trained back then was in 1970. 38 years ago. And that one I regretted doing, even if it was for my dear daughter. We sold it.
I did not ride, or as far as I can recall even touch a horse until a year ago September.
I am perfectly willing to find through AND that horses cannot be ridden without pain and injury, and never ride again myself. But I'll still be what I call now, Servant to the Horse.
And hope that he will accept me as a friend. This is more important than riding.
There is plenty in that for me. I don't really need to ride ever again.
My job now is to find others and teach them about this discovery.