A braces fetish is a little kinky and it can be somewhat embarrassing, but "ashamed" and "horrible" are pretty strong words. I really hope you do not beat yourself up that much over your feelings. It is understandable that some people with a genuine need for orthodontic care can be annoyed with those who fetishize their medical problem. After all, they are putting a lot of time, effort, and money into something that might be very uncomfortable and inconvenient for them. From their perspective, it is baffling to them as to why someone would idolize something that they would rather not have to endure. But as long as a braces fetishist has respect and sympathy for what a real patient has to go through, I think that respect can become mutual. Everyone has their kinks, and provided of course that those kinks are explored between consenting adults, it is silly for someone to degrade another for what gets them off. I am sure there are plenty of orthodontic patients who hate their braces but have a fur suit, or ropes on the bedposts, or a drawer full of toys.
Perhaps a little soul searching might be in order to help figure yourself out better. You did mention an abusive childhood, so some therapy could help you if you have not sought it out already. You also have a couple of posts saying that you want to meet others wearing braces. I am pretty confident that you could find LOTS of people with braces at say- an orthodontist's clinic? If you go to one and get active treatment for yourself, you will have a couple of years worth of appointments during which you could meet someone. And since you would be wearing braces as well, it would be a shared experience with that someone, which could alleviate some of the guilt that you are feeling. Besides, it also might be a lot of fun!
HTH