Because he destroyed our constitution and committed insane war crimes because he thought the Union was for “the greater good”. Our country has never been the same since. Getting students to view his emergency efforts as noble basically justifies any action you can convince them is virtuous, no matter how violent or unconstitutional.

Lots of material at Mises.org. Lincoln’s Quest for Empire is a doc that just came out, but you gotta pay. Lincoln Unmasked by DiLorenzo is a good book.