You always have to be open to criticism and not fight it. If you're resistant to feedback and changes, then you're slowing down the process. You might disagree with the direction of the shot and the changes that you are being asked to make, but at the end of the day you are doing work for hire. You are being paid to bring someone else's vision to life. So you have to leave your ego at home when you go to work. That, to me, is the bottom line. You don't want to be the guy that goes, "That's stupid feedback, I'm not going to do that."
It's important to remember that it is not YOUR portfolio you're working on, but the DIRECTOR's portfolio (or whoever is calling the shots), but it's really not a common thing to go back to your desk after dailies cursing at your notes. And sometimes you disagree with the feedback but then when you watch the movie, you realize that in the grand scheme of things it was the right choice. It's easy to just focus on your shot and not think about the sequence or the whole movie, but the person in charge has the overview and he or she is more aware of how the whole thing plays out. So you also have to trust the director.
You can absolutely disagree with someone's critique and as long as you bring it up in a polite and constructive way I think it's okay. I wouldn't just say no to the feedback, of course. Try to bring another idea to the table. Try to find another solution instead of just disagreeing.
You should also be aware of the production schedule. If you start a movie, then there is enough time to talk about shots and brainstorm. But if you get a change during crunch time and you're in the final stretch, then it's not really the right moment to start a discussion. Everybody might know that the feedback is not the best, but it's about finishing the movie at that time, so you have to put your thoughts on the backseat. Pick your battles. :)