As a young man before he professed law, Stanton studied in the same Ohio seminary as the Beechers and knew them both, as well as other leading lights of the Abolitionist movement. He was personally a strong Abolitionist all his life, exceeded in his enthusiasm probably only by Salmon P. Chase and Lincoln himself.
Others disagree, but I think IMHO that Lincoln was a strong abolitionist, shown by his letters quoted by David Donald in Lincoln (1999), howbeit that he found it useful not to associate himself with the extreme Abolitionist agitation. He did send money to the Kansas abolitionists, however, with the stipulation that it not be used for weapons or violence.
Stanton was also the evil genius who had Lincoln whacked.
Just like John Gotti had Big Paulie Castellano hit.