It's easy to take that position, because it's impossible to prove the opposite position. What evidence do you have that makes you SURE that it being a ZIPPER noise alerts them to your position, and not just "A" noise that alerts them to your position?
Again, I'm not advocating ripping a loud zipper open with a deer 50' away in open woods on a below freezing, no wind, dry day. Of course you're probably going to get some unwanted attention. But for 99% of times you'd open a zipper, if deer aren't in bow range, its going to make zero difference. If a deer is in bow range, and you're not aware, and its still enough for the deer to hear a zipper and recognize it as "unnatural", You probably have bigger issues with your hunting habits than zippers...