Is your glass half full or half empty?

I've just read a blog post on this age-old subject. I used to be a "half full" type of person myself, yet was almost disgusted by the shiny optimism that gushed from the post and it's comments. And if that wasn't bad enough, they happily shot down the "half empty" philosophy without even understanding it.
I mean, when you first look at the subject, it's as obvious as black and white, optimist and pessimist. But are we so daft that deeper meaning escapes us? And even if deeper meaning was never intended, what's keeping us from looking for it?

Here's the comment I added, hoping that at least one person will understand or even relate:

'I'm a "half empty glass" gal and think our philosophy is highly missunderstood!

Yes, many of us tend to be dislikable since we are often - "I have everything I need but am not rich enough"-ers, or "proud to be a martyr" types, or "i'm just waiting for life to end and hope you'll join me in my depression" people. But what you don't see is that for many of us, this philosophy helps MOTIVATE us.
It helps us see that more can be achieved and once we have the strength to do so, we can try to achieve more.
A European Socialogist (can't remember his name) has explained this phenomenon which he feels explains "new" society: Before, society was content with simply providing for self and/or family. In a sense, survival and caring for the family was the purpose of life while happiness was only a bonus. Today however, society as a whole considers happiness to be the purpose of life. This complicates things since what makes us happy varies from one person to the next, and can change several times during a lifespan.

Here's MY explanation of this philosophy:
When a person like me observe that glass, we notice that it is half empty because we have drunk from that glass. And in reality, we can earn the right to refill the glass, but shhh, don't tell anyone. '