"Add a heavy dose of presentism (judging or interpreting the past according to the standards of the present), mix thoroughly and serve COLD to an unknowing, non-thinking viewing public and call it... HISTORY."
Vallante's definition of presentism isn't that far afield from the accepted. Merriam-Webster defines it as, "an attitude toward the past dominated by present-day attitudes and experiences." This sounds about how I might define the concept as well.
However, discussing the concept in the abstract does little good. Let's apply it to a strawman problem, one to which the neo-confederate crowd applies it quite regularly: slavery. Whenever the moral inequities of slavery or the cruelties of the system are elucidated by a scholar or public historian, the ready retort is typically an argument that slavery can't be viewed from a presentist perspective. The rebuttal is typically phrased in the simple pronouncement, "that was the morals of their society," or even more simply, "that's just the way things were back then."
In some manner, this is a laudable effort. Viewing the past from a perceived viewpoint in the past is a distinctly postmodern way of looking at the world. It is viewing the world from the shoes of the past. But are those shoes actual Civil War era brogans, or are they a modern reproduced facsimile? What were the, "morals of their society?" What was, "the way things were back then?"
Certainly, slavery was legal. It was morally accepted by a chunk of the nation, North and South, as a viable option. But do we measure a society's intellectual and moral advancement by its best or its worst traits? The inter-war period in Europe spawned Adolph Hitler, Benito Mussolini and Neville Chamberlain. Do we as a world judge that generation by it's murderers and appeasers, or by it's brave members who charged a beach at Normandy to fight for the freedom of the oppressed? I come from a generation which spawned Eric Harris and Dylan Klebold. Do I measure my generation's advancement simply by their violent rampage, or do I look to the good folks of my generation who are working for the betterment of society? I would argue that a society is typically measured by its greatest achievements, be they technological, moral or philosophical. It is not the mundane which characterizes a society. It is not its worst elements. It is, instead, it's most advanced. The Bronze Age is known as such because the most advanced metalworking abilities in the culture were composed of copper and tin. The Age of Reason/Enlightenment is known as such because the most advanced intellectual concepts were centered around reason.
What, then, were the most advanced thoughts on the extent of the freedom of man, the furthest reach of intellectual progress, in the 1850s and 60s? Could these decades be deemed the Age of Abolitionism and Suffrage, with the most advanced thought on freedom in America being that it was universal and should not be restricted by race or sex?
If I were to posit that all slaveholders could and should have easily emancipated their slaves any day, the response would come from a general audience that that concept just didn't exist in the 1850s. But that vision of America is patently wrong. The concept of immediate emancipation in the face of moral evil did exist, as one of the cutting edge views of the definition of freedom.
Frederick Douglass, himself a former slave, protested throughout his free life against the inequity of the system of slavery. He envisioned a different America than that in which he lived. In 1845, he told a crowd in Limerick, Ireland that, "the Americans, as a nation, were guilty of the foul crime of slavery, whatever might be their hypocritical vaunts of freedom." The dream of a republican nation had been lost; "it was not a true democracy, but a bastard republicanism that enslaved one-sixth of the population.—They were free booters who wished to be free to plunder every one within their reach." Douglass was keen to let the American nation know that, "a slave had stood up in Limerick and ridiculed their democracy and their liberty."
Douglass told a tale of the indignation he saw when he, "took up a book and quoted from it the laws of the slaveholding states," to a group of slaveholders on a ship to the United Kingdom. "A spark of fire thrown into a magazine could not have produced a greater explosion," he recounted, "They could not bear to have the iniquities of slavery exposed, and they reared up against him like demons." The deep indignation shown by this group against the laws they and their ilk had crafted to protect the peculiar institution could be interpreted as subconscious guilt at their continuance of the enslavement of that 1/6th of a nation.
William Lloyd Garrison, Boston's prince of abolitionism, likewise showed open intellectual disdain for America's institution. By the 1850s, the masthead of his Liberator proclaimed each week that he would have, "No Union with Slaveholders," and that "our Countrymen are all Mankind." Garrison famously and repeatedly proclaimed the Constitution, "the source and parent of all the other atrocities - 'a covenant with death, and an agreement with hell,'" burning copies of the foundational document to cheers of, "Amen!" from like-minded Northerners. After the passage of the Fugitive Slave Act of 1850, he began burning it too on stage with dramatic flourish. Garrison heartily believed that the nation had strayed into the territory of evil and wickedness for its embrace of the institution of slavery. He vocally urged for nearly four decades that slavery was wrong. His voice mingled with those of men like Reverend Samuel May of Syracuse, NY, who damned slavery as an anti-christian institution, ignoring the supreme law of Christ's teaching. His hands worked along side those of men like Gerrit Smith, who bought tracts of land with his own family fortune all across Upstate New York explicitly to set up freedmen's communities to harbor the freight ferried Northward by the Underground Railroad.
The existence of a Frederick Douglass or a William Lloyd Garrison, of a Samuel May or a Gerrit Smith, invalidates the cries of "presentism" when we damn slave holders for holding slaves. The institution of slavery in the 1840s and 1850s were rife with men and women who felt slavery wrong, immoral and evil. It was not a nation blindly accepting the vile institution which held 4 million in bondage. The bare truth of the matter is that the advanced and modern thought that people should never be property, but should have universal freedom, existed and thrived in the 19th century. So to did the backward and sinful thought the man should be no more than property, no better than dog. But the impulse of freedom for all was the era's furthest reach of the slow human march of progress. It could be said to characterize the American intellectual meaning of the age itself. The very fact that these men could visualize a land without slavery means that those who clung to that system were inherently backward. Slaveholders were intellectual anachronisms in their own time, holding the line against the age's defining characteristic: progressing universal freedom.
Presentism might exist in historical study, but it certainly isn't us judging slaveholders as evil, immoral or unjust. That perspective is a distinctly period viewpoint, not one we impose from the realm of today.