I don't know, it's strange. Youtube and Facebook are bright, but I'm used to them being bright. I'm way too used to these forums being dark...and I like it that way.
Proof that you are a young'un. These forums didn't always default to a horrible dark theme. The tan theme was pretty bright, and the green and gray themes weren't really what I'd call dark either (the green one was darker than the gray one, though)
When I joined this forum there were 5 or 6 themes, compared to the sparse pickings we have now...