I'm always interested in this debate because I think it reveals something about the general question of how to evaluate politicians. When you look at the career of Abraham Lincoln, you see a guy who joined the more slavery-skeptical of the two political parties. As a member of the Illinois state legislature, he opposed the short-lived effort to bring slavery to the state. As a member of congress he criticized the Mexican War as a slave power land-grab and backed the anti-slavery Wilmot Proviso.He got back into politics to criticize the Kansas-Nebraska Act as too favorable to slavery. He helped found a new anti-slavery political party. He ran for Senate in 1858 as a member of the new anti-slavery party and criticized his opponent as an appeaser of the pernicious slave power. Then he ran for president in 1860 as the nominee of the new anti-slavery party against a number of candidate who all warned, accurately, that his election would precipitate secession. Then when his election did precipitate secession, he implemented a policy of military coercion against the seceding states rather than compromise on slavery even though he knew this would prompt even more states to secede. Then he fought and won a war against the seceded states, during the course of which he freed the slaves!On the other side of the ledger, you have the fact that he spent a lot of time saying that he was only interested in saving the union. But the entire point of the Republican Party was to break the hold of slaveowners over the national government at the cost of provoking sectional conflict. There was a whole other political party--the Democratic Party--organized around the principles of white supremacy and sectional accommodation and it's a party Lincoln never belonged to.
Save your eyes. Take breaks.