In any professional endeavor, there are going to be disagreements between those involved. Writing is no different. As much as it's an exciting time to be an author, it's also a scary time to be one of those people taking the risks with your money and reputation. So everyone wants to be certain that each new book is the best it can possibly be.
So what happens when someone tells you that you need to change something you've written? It's going to happen. Whether agent, publisher, editor, or beta reader, at some point someone you depend on to help you get your work perfected is going to say something you don't want to hear.
Your hero is too bland. You don't have enough description. You have too much description. They can't empathize with the hero. The story is too similar to another book. The story is too different from other books.
There will be times when it feels like you can't win. Like no matter what you do, someone is going to disagree with your decisions.
And you know what? You're right. No matter how good you are, someone out there thinks you got it wrong or that they can do better. You just have to live with that. Take lessons from the sensible comments, grow a thicker skin for the rest, and move on.
But it's different when someone you're working with says something like that. You have to remember that the people providing you with the feedback are on your team. They all want Team You to win and be successful. They also have a stake in making sure of it, because if your book fails, that reflects badly on them. Whether as friends, as freelancers, or the staff of a publishing house, they share in the results of your work.
Before responding, make sure of one very important thing. Check to see whether their comments have simply hurt your feelings, or whether you genuinely believe they're wrong. If it's the first, odds are good you should make that change, and thank them for helping you learn. If it's the second, and making the change might damage the book, then for goodness' sake, do not pounce on them with a purely emotive response.
No, take your time. Be respectful. This is a person who cares enough about your work to tell you something you don't want to hear. How many people in your life can you genuinely rely on to hurt your feelings for your own good? Those people are dear to you, whether you think it or not. They're willing to risk your wrath because they believe it will help.
Answer their comments with tact, courtesy, and grace. Open a dialogue. Talk. Ask them why they felt this way, and ask for their help in fixing the problem. Remember that it's not black and white. Feedback can have both issues to be addressed and points to let slide, so be sure to keep an open mind and never, ever forget this important rule:
You are always the student, and there is always a teacher. When the teacher appears, accept that you have something new to learn and embrace it.
I speak from experience. Sometimes the most terrifying criticisms can become the most important lessons.