It wasn’t about anti-abolitionism or it never would have gotten the nod from anyone who wasn’t pro-chattel slavery. And what do they do about hireling? The point is that the opponent had no real support. Maybe yhey could still change slave to knave to avert even that confusion.
You are falling in with the ‘think’ and ‘history’ crowd. None of the snowflakes ave any more idea of what a knave was then they do about the Civil War. ‘Knave’ is to them likely a white racist term ...