Many modern historians do not consider Gettysburg the turning point you mention, I must say that I adhere to that line of thinking. Basic argument is that we now know it had an impact but at the time of the Civil War consequences were not at all that clear. The Union Army repulsed Lee's army but failed to pursue it and destroy it and still today is debated whether Union Forces were in fact capable of doing so as they suffered equally heavy losses.

We know that Lee suffered a severe attrition and would never recover the initiative again nor the offensive but at that time he was not criticized by the Southern public opinion and his troops remained strongly loyal to him.

I'd say the Emancipation Proclamation had a deeper impact at the time, Lincoln meant business and clearly targeted the heart of the Southern economy and social structure, he also sent a message to foreign powers in this sense, something like "if you support the rebel States" you are only against the Union but supporting slavery.

I would say that the Emancipation Proclamation is a turning point, in that up until that point the war may have swung either way, and that Gettysburg was the beginning of the end, in that after that point the already-doomed Confederacy was put on the fast track.

The Emancipation Proclamation is a turning point because it kept foreign powers out of the war, which was one of the few true hopes of the Confederacy. It also paved the way for black enlistment in the Union Army, which provided a much-needed manpower boost in 1864 and 65. By the end of the war 10% of Union soldiers were black.

Gettysburg was the beginning of the end for the Confederacy--the high tide. Immediately after the battle soldiers began to write about its significance. But just because a tide creeps higher up the shore doesn't mean you should expect a flood to follow. Even a lopsided Confederate victory at Gettysburg probably would not have resulted in the loss of Washington or Baltimore. The battle had tactical significance, but the South was so far behind in strategic issues (misfiring economy, acrimonious politics, stagnant commerce) by that point that I don't think one can say that the eventual outcome of the war turned on Gettysburg. The horrendous losses and tactical setback of Gettysburg certainly sped the Confederacy towards its doom, though.