Yeah it's not fair to blame the european conquistadors for the disease they brought over, they weren't to know.
The totally unnecessary brutality however, is another case.
We Europeans seemed to have sent our most aggressive men over to the New World to form our colony. Men who love violence and guns. And so it remains. You have mass shootings every week. Either you blame the guns or you blame the people - surely you'd rather you blamed the guns otherwise you're admitting your nation is uncivilised.
Our other colonies in Australia were a bunch of convicts yet have formed a more civilised society than America.