I own a horse that was trained/started with rollkur. It took me a few days/weeks to get him to even try to stretch down and out properly. It is a terrible thing to do to a horse, and if it is done too long the effects on the horse's body and mind are irreversible. I know it is unwise to compare people to humans, but I would never tell my horse to do something that I would find painful (except for things like vaccinations etc). This includes running with your head crammed against your chest for an hour.
It is one thing to dislike rollkur, it is another to feel with your own hands what a horse that was trained with the method is like. Because I have felt my horse who was abused by heavy handed riders, I could feel his fear when I gathered up the reins, his desire to avoid being on the bit, the stiffness in his neck and back. Rollkur is performed by taking a horse that is above the bit and hollow, pulling hard, forcing them to go fast, see-sawing and yanking on the reins, and then the horse will compensate by curling under the bit and being tense. I do not know this from doing it myself, it is what I have seen with my very own eyes. People who do use such a method do not understand horses at all. All they understand is the color of a first place ribbon. I recognized his fear of the reins in seconds after mounting him. They told me that it was because he was young, because he isn't quite "finished" yet. That is one of the main reasons I bought him, he was at a big prestigious showing barn and chances are if I didn't buy him he would go to another showing rollkur owner and have an unhappy life.