Progressives are insane. They want to celebrate something that did NOTNING! The Emancipation Proclamation freed NO ONE! It only applied to states that were in open rebellion, and over which Lincoln had no authority; and at that it excluded sections of those states that were under Union control (such as some Louisiana parishes). It did not apply to slave states that had not seceded (for instance, Delaware, Maryland, Kentucky). So, the EC did nothing as far as emancipation, as Lincoln knew it wouldn’t; but, he hoped that the EC would incentivize slaves to revolt and thus create a headache for the Confederacy. Slavery was not abolished until the ratification of the 13th Amendment, AFTER the Civil War.
Another major incentive was to keep Britain and France from recognizing and supporting the Confederacy. Making emancipation an explicit war aim was meant to move public opinion in those countries to support the Union.