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I can't take the name "Chris Morgan", because there's another user with that name. Why? Surely this value is only used for display and my email address is the only thing it really cares about?
Stack Exchange permit the display name to be anything you like, whether or not someone already uses that name. That is a sensible approach.
I can be ChrisMorgan, but I'd rather be Chris Morgan.
You're right, we should allow duplicate display names, especially now that the community is growing larger. I raised an improvement ticket here: https://jira.atlassian.com/browse/ANSWERS-807
I'll try to improve this in one of the next releases, to be continued :)
I suggest that you open a feature request for this. You can do this by clicking on the Add a feature request link at the footer of the site.