These morons don't even know our own state's history, or they just don't care
Yes, Tennessee joined the confederacy but it was the last state to do so and the first state to rejoin the union. The state itself was pretty evenly split on the issue of secession and abolition. Much of eastern TN were strong supporters of the union. There were Tennessee troops on both sides of the war and, in some cases, quite literally fought brother against brother.
Personally, I believe all that "heritage not hate" crap is a front for their craven racism. They want to live in a world where the white, Protestant, men rule over society and women and minorities are expected to show fealty. Any action that bucks that deeply engrained belief is sure to set these types off, thus their overreaction to protests at the state capitol and their actions against the TN three.