What's there to disagree on? He didn't want to fully commit to the abolitionist standpoint right away. He even suggested a plan to just ship slaves away and help them colonize elsewhere. What his chief concern at first was holding the Republic together. He would entertain any notion to do so.
He was elected on a platform of not extending slavery into the territories, and of not altering slavery where it existed. To commit to an abolitionist policy at the outset of the war would have forfeited popular support. Abolitionism was the policy of only a small minority of Northern voters in 1860; most of the votes for Lincoln had come from people that thought it was okay that slavery was still a Thing. A President is not and has never been a dictator, and cannot do what a dictator would do. Had Lincoln tried to executive-order slavery away at the outset, he would have faced a direct challenge from the Supreme Court on its constitutionality and probably a direct challenge from the Congress because that wasn't what most Congressmen signed up for. Avoiding certain legal defeat isn't dilly-dallying. That legal defeat would have imposed a cost, and would have restricted the administration's ability to set later policy. Better to wait until public opinion in favor of emancipation could grow. Better to wait until Chief Justice Taney died and an antislavery man could be appointed in his place. Better to wait until the situation on the ground changed so much that it would be impossible to
keep the emancipation genie back in the bottle no matter how hard the politicians at home tried.
Even though Lincoln followed a formal policy in Washington of not following through with emancipation, the reality in the field was drastically different. Only a few weeks after the attack on Fort Sumter, the first escaped slaves made their way through the lines at Fortress Monroe, and the initiative of the commander on the spot, Benjamin Butler, created the policy of seizing slaves as "contraband of war" on the grounds that they were being used to aid a military rebellion against the lawfully constituted United States government. It took a fair amount of hemming and hawing, but this contraband legal argument
was accepted by the Lincoln administration and deployed successfully later on. Lincoln had to rein in a number of commanders who tried to go further (David Hunter, John Frémont), but that was more out of fear that to allow them to make proclamations outright ending slavery would arouse the ire of the non-Radicals in Congress and of the Supreme Court.
Yeah, Lincoln came up with a colonization plan, and yeah he later swung away from that on the advice of some abolitionist leaders. Sure. Other contemporary abolitionists thought that colonization was a perfectly fine idea and an equitable solution to the country's difficulties. Lincoln himself took an extreme interest in the prototype colonization plan that was started in the Caribbean during the war, with an eye toward making sure that it would work out well for
everybody involved, blacks included. When it didn't, he scrapped the idea. It's hard for me to see how that's obviously morally unjust.
You say that Lincoln "dilly-dallied" before he "gave in to the abolitionists". That implies that, had he wanted to implement a policy of emancipation, he could have realistically done things in another, faster way. I don't see how that's plausible. He allowed, and eventually endorsed, the policy of war contraband essentially from the outbreak of the war. He tried a number of schemes - compensated emancipation in Delaware, relocating former slaves abroad - designed to settle the slavery and race issues peacefully and amicably to the benefit of both sides, before eventually settling on the emancipation program that we saw. As it was, he had to hammer it through Congress and through the court of public opinion every step of the way. Even the Thirteenth Amendment, famously, almost lost out on the floor of the House of Representatives, and that was in 1865 when it should have been eminently clear to everybody involved that the war was fundamentally about slavery.
I mean, I'd be the first one to point out that Lincoln was no saint; the man was the leader of a nation at war, who (however reluctantly) sent men to fight and kill and die in the hundreds of thousands. Condemning him for his political efforts on slavery, I think, misses the mark.