Say you have doubts, and that you want to discuss them. Then discuss them, in an orderly and dispassionate way. Keep in mind the possibility that you are the one who's wrong, and you'll be fine. Be calm, rational and modest.
Also: creativity does not mean not rejecting ideas. Creativity involves rejecting vast quantities of ideas. It just also involves creating more ideas than you reject. So one important phase of being creative is uncritically spawning vast numbers of ideas. Another important phase is critically evaluating them. Hemingway (apparently - this is potentially apocryphal) said "I write one page of masterpiece to ninety-one pages of shit. I try to throw the shit in the wastebasket."
Also: creativity does not mean not rejecting ideas. Creativity involves rejecting vast quantities of ideas. It just also involves creating more ideas than you reject. So one important phase of being creative is uncritically spawning vast numbers of ideas. Another important phase is critically evaluating them. Hemingway (apparently - this is potentially apocryphal) said "I write one page of masterpiece to ninety-one pages of shit. I try to throw the shit in the wastebasket."