For the most part, eugenics does not have a mixed history. Eugenics has a bad name because it has historically been preformed by eliminating people from the gene pool -- through murder or sterilization. As far as I am aware, no significant eugenics movement has avoided this, and therefor the history would not qualify as mixed.

We should assume that future attempts will be better when those future attempts involve well developed, well understood, well tested, and widely (preferably universally) available changes to humans before they are born -- that is, changes that do not take anyone out of the gene pool.