Blame the English language. Someone who says that we fought in WWII to free France or Belgium or to liberate those in concentration camps is wrong if the meaning is that that was our purpose in getting into the war or the reason why soldiers fought, but right in that this was one of the results of our involvement in that war. In other words "to" refers not to the initial purpose but to the final result. It may be misleading, but it's not an invalid use of the language or a false view of history.
The argument on the other side seems to be that the slaves were going to be freed "sooner or later" if the South had just been "left alone." Probably much later rather than sooner. From our post-Cold war perch in history we can delude ourselves into thinking that "eventually" things would always work out right whether or not people took action. But it's a delusion. People have to make decisions based on what they know and can see at the time.
The proclamation, contrary to popular belief, only freed slaves in states that were in opposition to the federal government and not controlled by union forces. All slaves in northern controlled areas were not freed by this, which included a large number of blacks in Maryland, Delaware, Pennsylvania, Missouri, Kentucky, and western Virginia.
Blame the Constitution. The government couldn't simply take the slaves away from loyal slaveowners. A constitutional amendment was necessary. But using its war powers it could announce that slaves in rebel areas would be free. And when US troops arrived there they were. Looked at one way, it was a simple refusal to return slaves to their masters or enforce slave laws, but it was quite a momentous step.
So much of the Confederate propaganda circulating today cuts the Emancipation Proclamation out of its context, but that distorts things. One can't pretend that no subsequent steps were taken against slavery. One has to see the Proclamation in its context as a step on the way to the 13th Amendment which did bar slavery. Alan Guelzo's recent book tries to do just that.
Pennsylvania had no slaves in the 1860s. Under Quaker influence they'd abolished slave labor in 1780. 18th century Pennsylvanians and 19th century unionists didn't have the ideal racial attitudes by 21st century standards, but emancipation was a momentous step and a great moral achievement. Simply dismissing or condemning such achievements undercuts America's political tradition, and leaves us with only desperate radicals, defensive or complacent slaveowners, and the indifferent.
I suppose the point in posting the article was to point out "Northern hypocrisy." But if one's only concern with slavery is "Northern hypocrisy" than that is in itself a form of special pleading and distortion. There was plenty of hypocrisy to go around in 19th century America, North and South.
Was it hypocritical for Northerners to condemn slavery in the South if slavery had been legal in the North in their fathers' or grandfathers' days? If so, such hypocrisy is inevitable, whenever improvements are made in social arrangements. Are we hypocritical to oppose Islamic treatment of women if our ancestors came from countries with similar customs? Once we're all up to speed on the hypocrisy of the freedom to own slaves, and really address that question, we can talk about the nuances.
But Lincoln's preliminary Emancipation Proclamation, issued in Sept 1862, gave the "...South four months to stop rebelling, threatening to emancipate their slaves if they continued to fight, promising to leave slavery untouched in states that came over to the North : ...."
[ A People's History of the Unaited States, 1492 - Present , Howard Zinn, p 187 ]
That is an extremely Machiavellian point of view. We fought WWII to defeat an evil that would seek to destroy all peace loving people. The invasion of the South was to force southerners to remain under federal control. The positive byproduct of an end to slavery was already on its way to being quickly acheived, and would have been accomplished in a way that did not destroy a society and leave the freed slaves in a position of serfdom. Had Lincoln been so concerned with obeying the Constitution he would have seen that in Article 1, Section 10, the rights denied to the states, it does not prohibit secession.