We've already collected DNA samples from people around the world to map the genome, it's how we even know what genes may cause disorders in the first place. This did not require us to create some genetically 'pure' hypothetical gene sequence for the ideal human. What you're suggesting is still eugenics and still bad for all the same reasons.

There may be such a thing as an "average" human genome though I doubt such an amalgamation would be able to produce a viable or even desirable organism. There is absolutely no such thing as a "clean" human genome, and attempting to create one would be a damning demonstration of a deep misunderstanding of both evolution and biology in general.