Smarties hailing from different backgrounds (and/or with different ways of thinking) working together is much more effective than separated, homogenous groups of smarties in almost every way. After all, there are many different kinds of smart and mixing them up results in amazing things.
You've probably read how small, cross-functional teams are much more effective than your typical silo-ed team approach. I believe that to be true. But there is more to it than that. Cross-function is one part, but it's also important to create diversity within a particular function. Not all designers are alike, not all engineers think the same way, etc. When you find a group of smart people that share a vision, but offer up different ideas on how to get there, that's when the magic really happens.
I'm calling this “Collaborative Diversity” and I think it's a great way to work.
Look at a company like Google. They would not be where they are today without bringing the best minds—from a very wide variety of backgrounds all over the world—together. Their employes have shared values and a clear mission: to organize and make accessible the worlds information. They also clearly value diversity and collaboration. If you look around at those doing amazing things, you'll usually see this. I love this bit pulled from their culture page:
It’s really the people that make Google the kind of company it is. We hire people who are smart and determined, and we favor ability over experience. Although Googlers share common goals and visions for the company, we hail from all walks of life and speak dozens of languages, reflecting the global audience that we serve.
More often you'll see culture clash producing mediocrity or failure. Especially when there are large groups with little diversity or, just as common, diverse teams not working together with intent, or unifying under shared values.
Or worse, working against each other. Congress might be a good example of that, as Vint Cerf illustrates in this great episode of DecodeDC. I suppose you could argue that Congress doesn't have much diversity, but I think what they're really lacking is collaboration, vision and unified intent. My guess, in general, they do share common values, but who knows? It's politics and things are a bit murky.
It's important to note that this kind of collaboration doesn't come without conflict. It's ok to clash, as long as your united in vision and purpose and use those differing points of view to move forward towards a goal.
It's not easy, but it is better.