My gelding has the best manners when my trainer, her husband, my daughter, or myself handle him, but when others at the barn go to turn him out or bring him in he misbehaves. He will trot circles around them, bite the other horse, etc. I wish they would correct him and stop complaining. He knows he can get away with it and does. I appreciate it when someone who is handling my horse corrects his misbehavior. We don't use stud chains at our barn, but all of our horses are trained with Clinton Anderson methods, so the way we correct them is different, but I wouldn't have a problem with someone disciplining my horse when he misbehaves. It is not okay for a horse to kick at, rear up, or act up when being led. They need correction.
Now, did you know that they use stud chains? If you don't like the training styles at the barn, you may have to change barns unless you want no one else to ever come in contact with your horse. You have to be comfortable with the people who are handling your horse, but you also have to accept when the correct misbehavior. Have you provided a rope halter for them to use?
And I doubt your horse is ruined. It takes more than one correction to ruin a horse.