There are three major reasons why modern Leftists try to denigrate Abraham Lincoln's anti-slavery goals and policies:
This is an expansion of a comment I made to
melvin_udall in
http://melvin-udall.livejournal.com/1085260.html?view=6828876#t6828876 regarding the American Left's obsessive denigration of Abraham Lincoln and specifically Lincoln's abolition of slavery.
I. An Inconvenient Truth
The first reason is that Lincoln, and the Republican Party in general, came to power with the avowed goal of ending slavery, a goal which they actually achieved in Lincoln's Presidency and within little more than a decade of the Republican Party's creation. The Democratic Party was the party of black slavery and white supremacy, and remained so not only to the end of the American Civil War, but in fact until after the passage of the American Civil Rights Act of 1964 -- at which point continued support for white supremacy would have been political suicide.
This not exactly something which the present-day Democratic Party, despite its strong historic ties to the pre-1965 Democratic Party, wants to be remembered. Any focus on Lincoln as the Great Emancipator is bound to lead to an awareness of just who it was that opposed them. Hence, it is important that Lincoln be vilified.
Political convenience is more important to the Left than is historical reality.
II. Panic in the Year Zero
The Left is constantly "re-inventing" itself and trying to win propaganda victories by devising new "standards" and then attacking others for failing to "meet" these standards. Lincoln was, by the standards of 1860, as close to a radical Abolitionist as stood a chance of being elected. But, because he failed to speak to meet the political standards of 2010, he's rejected as a "racist."
It's irrelevant that Lincoln acted on his principles rather than a desire to please posterity, whose preferences in any case he could not possibly have known. In fact, it's worse that he acted on his principles, because principles get in the way of rapid changing of one's colors to please the intellectual fashion of the moment. Were Lincoln alive today, and aware of today's ideologies, he well might still be politic, but he would almost certainly not be politically correct.
Intellectual independence scares the Left.
III. Words Count Not Actions
Anyone criticizing Lincoln for not really wanting to end slavery has to face one huge inconvenient fact: he is, in fact, the President who ended slavery. By executive fiat, no less, which means he was taking a serious political risk in doing so. But then if words count rather than actions, who cares? Lincoln failed to mouth the words to please the Leftist audience of 2010, and that's all that matters.
What difference does it make that said Leftist audience, rather than ending the chattel slavery still practiced in 2010, instead has come up with "multicultural" reasons why we should accept it in silence? It's not as if actions are relevant to anything, right?
Which goes far to explain the Left's current impotence in the practical world.