That seems like a simplistic and misleading dichotomy. Among those with interest in the subject, there were many Christians who were not fundamentalists, and many secularists who were not racist white supremacists.
I don't disagree with that. But, respectfully, make sure you're not falling for the straw man argument. As I said in my post you replied to, there were some Christians who argued the same thing as the secularists. That doesn't change the point that for the most part it was a church movement that was arguing for the 14th Amendment's "equal treatment of the law" to being implemented as stated (same rules across races).
For example, in the 1920s I believe it was the Methodists and Episcopalian churches who promoted eugenics. While the more "fundamental" churches (including Catholic) were against eugenics. Fortunately, the fundamentalist churches were on the rise.
If Wikipedia is to be believed, the eugenics movement was funded largely from the Carnegie Institution, Rockefeller Foundation, and Kellogg.
So except for a few exceptions on each side (again, not falling for the straw man argument), for the most part it was Christian fundamentalists vs secularist institutions.