Matt Ridley's Rational Optimist was highly recommended by one of my favorite economics blogs. It basically says what I would say if I had to defend my optimism.
Esp the chapter based on John Stuart mills quote from the 1700s
“I have observed that not the man who hopes, when others despair, but the man who despairs when others hope, is admired by a large class of persons as a sage.”
He does a good job documenting the history of pessimism in every generation for hundreds of years from Malthus and beyond. Even though statistically pretty much everything has been and is continuing to get better. The book is more of a string of anecdotes than data, but I do think his argument is right. It is rare to find a book in the book store that is optimistic (another favorite of mine, Lomborg's Skeptical Environmentalist is an exception that proves the rule--it got him widely and unfairly smeared by error strewn ignorant articles written in Scientific American and other venues).