Even though I'm a girl and, since I live in the U.S., have never been at risk of becoming circumcised I can understand why this would upset you. It was a part of your body and you didn't have the option to consent to it. There are reasons why this happens though, and hearing them may help you accept it. It's done when you are a baby because the procedure would be extremely uncomfortable and painful if it's done at an older age. Not that it isn't painful to babies, but you don't remember the experience afterwards. In America, it's an option to get it done, and it's normally done for the following reasons: it makes the penis easier to clean, is decreases the risk of urinary tract infections and STI's, decreased risk of penile cancer, and it prevents penile problems such as not being able to pull back the foreskin. So, in many cases, the benefits of male circumcision can outweigh the risks.
However, in many aboriginal tribes in Africa and Australia circumcision is used as a right of passage into manhood. It can be a religious or cultural ritual for Jewish and Islamic families or it can simply be family tradition. There are many reasons why men get circumcised, and knowing that it serves a purpose might help you accept it. Especially since it is medically useful.
With that being said, it's still not a neccesary procedure and it is the parents choice. I know that is frustrating, because it's still your body and as people we typically want control over our own bodies. I think it may help to look over your thoughts on this. For instance, you're mad because your foreskin was treated like a birth defect. In reality, it isn't a birth defect because every person with a penis is born with it. It wasn't taken off because foreskin was bad, just because it was potentially healthier for you. You're worried about missing out on pleasure. There have been many studies on whether circumcision reduces sensitivity in men, but the most prominent ones suggest that if there's any difference at all, it is minimal. Pleasure is centered in the brain, anyways.
This is just some food for thought. I find that thinking through my feelings helps me, it may not work for you but it's worth a try! You could also talk to your parents about this. After all, they are the ones that made the decision and they are the ones you're angry at. Talking through this with them could allow you to work through your feelings. Since you can't change the fact that the procedure was done, you can at least work through your thoughts and feeling about it so that you can eventually accept it and have it not bother you anymore.
I hope this helped!