I think most people take this in the wrong way... or in too much detail. Here is a more objective way of looking at it:
Just like within any group, lets take the example of a security guard, you have to wear a uniform. Granted its for a few hours, but as long as u are the guard, u wear the uniform. why? its the law/rule/etc.
Similarly, the hijab is a uniform for muslim women. There are rules for men clothing as well, but you dont see most men following that too. Anyway, so the hijab is the uniform for women while they are muslim. as being a muslim is a 24/7 deal, so is the hijab, with of course the conditions in which it is not required.
For those women who do it, more power to them. Those who dont, good for you. It is a matter of choice, in regards to what you want to do. But stating that hijab is not required, or debating its place in teh muslim world, that is wrong. If you dont want to do it, fine, but dont debate why its wrong. Just like you dont debate cheating on your spouse. it is wrong, but those who do it, its their choice.
hope this helps