I wouldn't suggest saying such things as "Over my dead body." Rather, politely consider what he or she is saying, but still stick to your gut and your heart. It may seem scary to want that, but hear me out. Something about life in general keeps me going back to that line in Hot Water Music's "It's Hard to Know": live your heart and never follow.
I'm sure almost all of my favorite books and movies encountered numerous skeptics in the birthing process from idea to finished product. So, to frame this stuff in my mind, I present to you possible feedback some of my favorite authors and writer/directors probably received:
"Gee George, a space action movie that's kind of a throwback to the serials from the Forties? Nobody watches those anymore. Hell, nobody remembers them. Besides, heroes in movies these days aren't heroic; they're dark, crooked and have major weaknesses. Anyway, is this a kids' movie or a movie for adults still acting like children? Seems like that audience isn't very wide at all."
"Jim, why can't you make a feature-length movie just like how The Muppet Show is? I mean, keep it on the stage and backstage with all the celebrity guests. A road movie with the Muppets just won't work."
"Jon, I think the script is funny, but could you make it more action-packed? How about setting it in Vegas? Does it really have to have all that mushy stuff in it? This is a gambling and partying movie, right?"
"Well Michael, these bands make for an interesting read, but none of them really broke through to the mainstream. How can you expect people who came in with Nirvana to really care about the bands that inspired them?"
This imagining can go on and on, but the point remains: get in touch with what your project is. You know the subject better than anyone else, so don't be surprised when someone -- who doesn't really know the topic at all -- suggests something outlandish. Besides, this is something you are attributed to with authorship, so you best well fight for what you want to fight for. It's worth everything in the long run.