Jason-
There are a lot of reasons that I love you man, and this post is just one of them.
This is a great question and it is the kind of question that HR leaders should wrestle with…but, based on what I see and hear they do not. They do not ask questions like this because 99% of conversations around diversity and inclusion are based on superstition, fairy tales and other forms of fiction…they are conversations full of platitudes and they are connected to nothing in the way of real action. Diversity and inclusion continue to be horribly misunderstood in the workplace and HR is no exception to this…the one thing that HR does know is that it does not want to say any of the “wrong” things about diversity. So…more loudly than any other part of the organization, HR talks about embracing, celebrating and leveraging diversity. And that is often the full extent of what they do. Some HR folks even resent having to talk about diversity, but that is all another topic.
A few points that I would make in response to your post and as a feeble attempt to answer your questions…
You said that conflict is not always a good thing and that too much conflict can be very bad. Agreed. And we need to make sure that individuals and teams have the tools to disagree in a functional and respectful manner…so that tension can actually lead to valuable outcomes. This is often missing…I have worked with teams ranging from front line service teams to senior leadership teams that are not willing or able to disagree in a functional way. This is incredibly dangerous to teams and organizations…dissent is a critical component in good decision making and problem solving. But it does have to be done in a respectful way, so there might need to be some ground rules put in place for how to disagree. The problem for most teams is not that they have too much disagreement or tension, but rather that they choose to be polite rather than honest and avoid all disagreement and conflict.
We also have to keep in mind what the nature of our challenge is…what is is that we are trying to accomplish? If we are going to pay the cost up front in the form of tension and disagreement, we must make sure that the juice is worth the squeeze. Are we trying to decide where to go for lunch, or are we trying to make decisions about how to implement a new strategic initiative, or are we debating about what the purpose of our organization is? Different outcomes worthy of varying amounts of difference.
We also need to make sure that once a decision has been reached that the team can come together and accept that decision moving forward…just as important as diversity is the ability for a group of people to move back and forth from divergent to convergent thinking. At some point we have to get back on the same page and put our disagreements aside.
You also asked about the right amount of diversity. When you really sink your fingers into the concept of diversity you realize that there is no way to measure it in any real way. Diversity is a big, contextual thing with a lot of layers and a lot of dimensions to it…there are maybe countless ways in which we can be different from each other and most of those ways cannot be measured or tracked in any real way. We should monitor the forms of diversity that can be measured because with that information we can look for evidence of intentional or unintentional barriers to diversity. But diversity cannot really be measured.
So, we cannot really talk about specific amounts of diversity, but additional diversity always brings additional potential into a group…it also brings additional cost as we have additional tension to work through.
You also mention the importance of commonalities. This is maybe paradoxical, but commonalities are a pretty big part of the diversity conversation. It is commonalities that hold us together…that is what we build the container with. The stronger the container, the more tension that it can contain. If we do not build a strong container, it does not take much difference, tension or disagreement to divide us…so part of our diversity efforts must be about taking time to reflect on the things that we have in common.
One of the tools that I like to introduce to help managers think about this is Glenda Eoyang’s Difference Matrix.

The Difference Matrix provides a framework for thinking about where a group of people are at with regards to sharing difference and the intensity of their interaction…and it points out some of the pros and cons of functioning in each of these four quadrants. As you mentioned Jason, we do not always want to be disagreeing, we do not always want to be about differences…that can be exhausting. But there are times when it is very valuable. So you can look at this diagram and think about your workgroup and what quadrant they are currently operating in

This diagram gives a little simple guidance for how to move a group from one quadrant to another…again, diversity (or difference) is important, but so is commonality and so is the ability to use both to move a group into different modes of functioning.
This post has gotten far too long already, but I am hoping there is something of value in there somewhere.
-joe
Joe,
You are right when you point out the many dimensions and aspects of diversity. This complexity does make it difficult–if not impossible–to answer Jason’s question with a number, formula, or other concrete answer.
As I read the conversation, I started to focus on this: We all have differences that get glossed over… we are actually more diverse in our teams than we may appear in the mirror. Thus the diversity question isn’t just about how to build a team with the “right mix” of commonalities and differences. It is also building a container that allows us to reveal the differences that are there–even when it may appear that we are more the same than different. Relationships, trust, low reactivity…
At this level, it is about differentiation of individuals as much as it is about the measurable and immeasurable characteristics of the group.