Oh hell... government!
But especially: interlocking metal teeth right where you have your softest skin -that's just one idea that should have ended on the factory floor!
Then again, you don't want a bunch of buttons in the way when you're in the bathroom and in a hurry. Unless you're worried about being caught with someone else's SO, why would you be in such a rush closing that part of your clothing? Getting "bitten" by a zipper strikes me as either carelessness dressing or recklessness about your personal relationships.