Animal rights people have a point that we humans may never do a perfect job of caring for our charges.
I don't agree with them that, because we can't be perfect, we should then not have animals to care for.
There are many kids and all kinds of people we should be caring for better, as there are horses.
We can't do a perfect job of caring for all, short of becoming other than we are and that may be an impossibility.
That doesn't mean we should not try, but that we be realists and know what we can work to do and what is pie in the sky thinking.
In other words, we can't make omelettes without breaking eggs.
If we want to use horses, we will have to understand that some just will always be unwanted.