Sometimes quotation marks - and the lack thereof - can get you into trouble.
When referring to slavery as "the peculiar institution" without the aforementioned punctuation marks, you run the risk of your readers inferring from the error that slavery was simply the peculiar institution that Senator John C. Calhoun (a slave owner himself) considered it to be - see his "Speech on the Reception of Abolition Petitions" (1837) - meaning a way of life that was simply unique or distinctive. As opposed to it being an institution that went beyond the bounds of acceptable human standards and practices.
Your error cheapens the value of the phrase.
And diminishes the impact that the establishment of slavery had on American history.
Two little punctuation marks.
From your editorial, "Slavery Museum: Dismay":
"Former Gov. Douglas Wilder had an excellent idea when he proposed a museum to tell a story that many Americans did not want told. Although slavery played as important a role in the American experiment as the Founding itself, until recently the peculiar institution and its aftermath have not received sufficient attention."
Ho hum. Slavery was peculiar.
Or not ho hum.
Slavery was, in fact, "peculiar" in that it existed in direct contravention of a quaint term you may have heard of in your history lessons. One taken from the bedrock principle upon which the United States of America was founded:
"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness."
Well, slaves were not equal. They - and the institution that kept them in bondage - were "peculiar" to our established form of governance.
It took 750,000 American deaths to end this "peculiarity."
Words, as they say, have meaning. So do punctuation marks. Ignore punctuation; ignore history.