If we did that then all of our historical figures would be so many mysoginistic racists. Times, values and ethics all change. The residential schools certainly weren't the only places of learning in which abuse occurred. Read Orwell's Such, Such Were the Joys. The strap was still common when I was a child in the early 60s, and my father was propositioned more than once by Catholic brothers when he was at school. 

Does any of this excuse behaviour we know to be wrong? Of course it doesn't. But it does help to explain it -- which helps to avoid repeating the same mistakes.  

Pat dismissals and expressions of distaste won't get us there, and neither will branding great men like Laurier or Trudeau as racist.