I wouldn't worry too much about that, because I don't see the whole of humanity having access to this technology. Their will remain an underclass who, in general, won't be allowed to have access to this (more due to economics and politics that don't allow access instead of direct prohibition of access, think about how medical care is currently allotted). I think the interesting bit will between what happens between those who have regular access to this technology and those who don't. Could there end up being two human species resulting from this?

Also, as someone else pointed out, it would be more likely we edit different lines of humans. Two people having the best genes for a soldier and having the best genes for a scientist are likely to be better off than a single individual who has the best possible maximum of the two together. Optimizing multiple lines of humans each on a smaller set of traits is likely to produce far better result than optimizing one line on all traits.