Aside from his occasional published pejoration, and arguing the case for abolition forcefully person to person on every occasion that arose, I'm not aware that Darwin engaged in any further activism specifically in opposition to slavery. He did support the missionary movement, both with donations and in laudatory writings, probably in part because it was generally abolitionist, but mainly because he saw missionaries as a civilizing force (both on natives and on the colonials).
Darwin was certainly justifiably proud of the contributions his family had made, principally on the Wedgewood side, to the abolitionist cause. E.g. his grandfather Josiah Wedgewood who (or rather whose workers) designed, mass produced and distributed this famous seal of the Society for Effecting the Abolition of the Slave Trade, of which Wedgewood was a member:
These widely distributed emblems were worn and displayed by abolitionists in both England and America, and turned out to play an important role in popularizing abolitionism and turning it into a mass movement.
Lessee. Also Darwin showed concern for the welfare, and justice concerning, former slaves in Jamaica. We was a member of the Jamaica Committee, organized in 1866, to prosecute Governor Eyre to be tried for his excesses (including the slaughter of innocents, summary executions without trials, etc) in putting down the "Morant Bay rebellion" (1865). Darwin was very energetic in fund raising for this cause. It was an issue that divided British society with many Tories (including much of the clergy) supporting Eyre.
But for the most part Darwin's charitable donations, voluntarism and activism, although considerable, where kept close to home, in Downe on Kent, where he carried out many projects for the poor, and for the benefit of ordinary folk, in cooperation with his close friend, the local Anglican pastor Brodie Innes.
There was enough of the eugenicist in him already for him to be losing any sleep over such matters as the suffering of his fellow human beings.
Not accurate at all. If anything Darwin was excessively empathetic.
“Nature is bloody in tooth and claw.”
Um, yeah. That -- "nature RED in tooth and claw" -- is from Alfred Lord Tennyson, the poet, and Christian, and was written in 1849, a decade before Darwin's Origin.
You're kinda snide regarding Darwin, but I don't think you have a very accurate appreciation of Darwin the person.