Is it the fur trader guy?
http://www.campbellhousemuseum.org/"While Robert supported the right of men to own slaves, he himself had emancipated his final slave several years before. In 1857, Robert freed his slave Eliza and her two sons, apparently because his wife Virginia had grown distasteful of the institution."
"Campbell was influential enough that he was elected as President of the Conditional Unionists at a city convention on January 12, 1861. The convention voted to support slavery as a constitutional right, and urging the Federal government to restrain from using force during the crisis."
That's in the context of the civil war, too, not the founding of the US, so it's quite a bit harder to justify. Leader of a group that advocated making having slaves a constitutional right? Even in the context of trying to prevent war from breaking out, that's... bad.
Still, reading through, it sounds like the dude was involved in enough frontier wars and politics that he's solidly a historic figure. So I retract my "not historic" comment. Hopefully the museum has some information about his slaves and his involvement in advocating for slavery.
I doubt the folks trying to burn it knew any of that, but then again, maybe they did. Guy owned slaves, advocated putting slavery in the constitution, ran a fur trading business, and spent a lot of time fighting native americans. You can find plenty of people who don't think highly of any of that.
-W