Pretty simple. Diversity is good. Not diversity in a Title 7 kind of way, but a balance of power related to how people think.
Too much of a single way of thinking in your company? You start thinking something like the Microsoft Zune is a good response to a competitive threat. Pass the Kool-Aid, Amigos. It sure is fun to be around people who only think like me.
Until it's not. Or until actual performance is desired.
I'm most comfortable with a balance of power. Dems in the White House and Senate? Not idea for a moderate Republican, but OK with the GOP maintaining the house. And by the way, probably better than the GOP having it all.
Want to get something done? When there's a balance of power, you're going to have to cut a deal and actually work with people who don't think like you. Which actually maximizes the chances that something good happens.
Balance of power related to how people think is what you want for your company as well. It's the most important type of diversity you can have.
PS - for all you Apple fanboys and girls out there, here's the Apple senior team pictured below. The good news is that I'd fit right in. The bad news is that this picture can cause bad PR. But the picture doesn't tell us whether they have the most important type of diversity, though...
Which is whether all the pictured people think the same way. Or think different.