I'm not so sure that Margaret Sanger saw it differently...she was deathly afraid of the "undesirables" reproducing at a faster rate than the "desirables"...she definitely saw the "danger" of "survival of the fittest" meaning "most likely to reproduce." That's why she pushed so hard for birth control.
I once spent some long hours going through roll after roll of microfilm, and printed the first in a series of my findings, before the publisher squashed it. The excerpts were too inflamatory.
Looking back at my original post I think I did a lousy job of phrasing what I intended to say (this is a sometimes unavoidable consequence of the internet).
What I meant to say is that Galton, Leonard Darwin and certainly Sanger saw eugenics as a method to limit the reproduction of those who they considered "undesirable."
Would Charles Darwin have agreed with this manipulation of his theories? Probably not, but the fact remains that prominent people, including his cousin and son, used his theories to advance racism.