A: It's to make you look cooler than you actually are. Also, it's to protect your eyes from the impending doom of the sun's fiery wrath.
A: Ha! You think you're going to space, huh? Newsflash, friend: bronze Sunglasses are for Earthlings. In space, we have Sunglasses-9000, the space-proof edition. (Ask your friendly neighborhood astronaut for details)
A: Oh, you want to be that guy? Sure, why not? Just don't say I didn't warn you when your bronze Sunglasses turn into a hat-astrophe.