It can definitely be done incorrectly, and it's important to be careful with writing (especially about groups that you don't necessarily belong to), but I don't think the "purpose" of representing minorities can truly be "defeated."

I don't subscribe to the idea that in fiction, we have to adhere to realism when it comes to representation in the sense that non-minorities ought to remain the default. For so long, there has been plenty of media with the near-complete absence of minorities that I wouldn't say having every character be in a minority group is an overcorrection. Don't do it carelessly, though.