Lincoln's support of blacks and freeing the slaves cost him his life. There's not a so called black "leader" today and certainly no one in the BLM crowd that would risk that much for their own people these days much less someone with a different skin color.
Lincoln was willing to militarily impose "union" on the secessionist states by conquest. Emancipation caused problems with northern conscripts as a casus belli
, more so than conquering the raw materials rich South for their Northern industrialists, who also saw industrialization in the South as a budding problem, but emancipation did not become the issue of record until the war had been going for years, and was an effort to cause slave uprisings in the South. Lincoln underestimated the familial ties between slaves and owners, and apparently believed the abolitionist agitprop like Uncle Tom's Cabin
was the norm, rather than the exception as far as treatment of the slaves went. It made no more sense to abuse slaves than it did to abuse livestock or draft animals, or to trash tractors and combines today, and slaves who were treated reasonably well formed loyalties toward their owners, so the expected rebellion did not occur. Yes, freedom is desirable, but carries numerous responsibilities with it, responsibilities many former slaves were either unprepared for or simply did not desire.
Considering that industrialization and mechanization would have eliminated the economic incentive to own slaves as surely as internal combustion engines eliminated draft animals, manumission would have come in the next few decades, and with it, the transition to full freedom might have been better accomplished, preparing those formerly owned for more full participation in the economy and society than sudden liberation by developing the education and skills needed to function in society.
We speak repeatedly of the current Democrat "Plantation", but that was enabled by a cultural and societal transition which many were unprepared for, and that transition still has lingering cultural aftereffects. Those who did best were (often surreptitiously) taught to read and do arithmetic, partly because they were more able to serve their masters, but also in anticipation of their eventual manumission. Keep in mind that I am writing this from the POV of a Marylander, where the slaves were being freed by their owners as the style of farming changed, with the growth of Washington D.C. and Baltimore requiring produce, and the need for slaves declining. Manumission was up prior to the War, but the Union did not free the slaves there until afterwards, guaranteeing a labor force for the Capital.
Booth saw Lincoln from a Southern perspective: the leader who militarily conquered a region and its several States to keep them in a union they did not want: a tyrant, and said as much when he shot him. ("Sic semper tyrannis" --
"thus always to tyrants". and the motto of Virginia, as ironic as that may be today) From the POV: There are no just powers when there is no consent of the governed to borrow phraseology from the Declaration of Independence, and slaves were regarded as property (and a considerable investment was needed to be an 'owner'. The States in secession had revoked their consent to be governed by a Government they saw as no longer serving their needs, and Lincoln's failure to stop the invasion of one state by others (MD invaded by PA and MA), and to respect the withdrawal of consent embodied in secession was the spark for war.
Slavery was an issue, but not the only one, by far.