I was talking the other day to a fellow writer who is terrified of the process of having a book edited. Particularly, she has a (quite legitimate, sadly, in today's market) fear that a publisher will label her book YA because the protagonist is under 18.
However, I'm going to set the YA thing aside for now and just say a few things about the editing process:
1. The publisher would not have accepted the book if they did not like it. Publishers get thousands of manuscripts and accept the tiniest fraction of them. They can afford to be extremely picky. So, you know they like it.
2. You and the editor have the same goal: Sell as many of the book as possible. Any change an editor suggests is designed to increase sales.
3. You can always walk away. If, for example, an editor demands you change something in a manner that you feel is censorship (like saying your bad guys can't make a racist comment in order to highlight that they're bad guys), you CAN get out of most contracts. If there's no clause to allow you to escape, try to negotiate one. It can be worth it with a novel (although generally not so much with short fiction...but the vast majority of short fiction editors demand the rewrites before sending the contract, in my experience, making it even easier to walk away).
But before you walk away, sleep on it. Talk about it with your best friend. Think about it carefully...because that contract might be the start of a beautiful career and while the editor is not always right, they often are.