I think you have have been severely misinformed and while you are totally entitled to your own opinion I think you need to properly informed on dressage. I personally take offense to this because I go out of my way to make sure my horses are moving naturally while training. My horses are never FORCED to collect or gain contact in the bridle this is something you can't really force without the horse's movement becoming hindered or restricted. Dressage is about getting your horse engaged with you and working as a team. Dressage LITERALLY means "training" and that is all it is, it is training. It is the right amounts of balance with horse and rider, rhythm, and timing. And is different with each horse and rider..
There should NEVER be any reason for anyone training in dressage to use chains of any sort. So you are almost certainly talking about gaited horses, Tennessee walkers, Saddlebreds, Paso Finos, etc. If you are using chains to alter your horse's movement in dressage you need to just quit riding and go back to the basics because you obviously missed something along the line..
So please do not bash something you do not understand or know. =] If you took the time you would find that dressage is a beautiful way of training horses and just like every other discipline there are those out there who will break and bend the rules and harm their horses to win ribbons..