The Globe editorial about Confederate monuments a few days ago put it well: 

"Those monstrous Confederate beliefs were not blemishes on an otherwise positive history. (That's why no one should favour removing statues of Washington or Jefferson). They were the fundamental principles of the economy, politics and laws of the Confederate States." 

Some of Sir John A.'s attitudes were just that - blemishes on an otherwise positive history (which he shared with most Canadians, by the way.)  The Elementary Teachers' Federation of Ontario is wrong on this.