Did TR think slavery was good for blacks? Nope, but Calhoun 120% did. He was definitely one of the guys citing the Bible as a justification, too.
Was TR a states' rights fanatic who supported nullification? Nope, not even close. Calhoun sure as hell did - he was a hardcore believer in federal minarchy. No question he'd have been the first to call for secession if he'd lived long enough.
The South lost. There's plenty of opportunity to teach kids about these fcksticks in the history books, without having any monuments in their honor. TR, despite his faults, did plenty that was good for America; Calhoun and his ilk wanted to maintain an oppressive and backwards society. Fck them, and let their statuary melt.
EDIT: Not to mention, quite possibly the worst case of Resting A55hole Face in American history. Seriously, he makes Andrew Jackson and Ted Cruz look likable.