Here's an interesting article from the Los Angeles Times (thanks, Cindy):
According to surveys, in developed countries discrimination against women and minorities is actually waning and gays remain the least tolerated "outgroup" in society. They are the proverbial canaries in the coal mine. In most developed countries, the relative level of their acceptance or rejection is a sensitive indicator of that society's overall tolerance toward minorities. And -- here's the takeaway -- social tolerance "broadens the range of choices available to people," thereby enhancing happiness for both the tolerant and the intolerant alike.
It's based on a study conducted at the University of Michigan by a team led by Ronald Inglehart. They found that freedom of choice is apparently a universal aspiration--and the single most important basis of human happiness. Change the law to give more people more freedom, more choice (e.g. make marriage legal for same-sex couples) and more people, not just gay people, are happier. Go read the article. It's kind of cool.