No one has ever said or suggested the North was without sins. And the premise, two wrongs make a right is demonic. You do NOT excuse bad behavior by pointing to someone else with bad behavior.
Turning now to the Small Pox Blanket hoax, let me set the record straight:
In about 1763 officers in the US Army purposely gave infected blankets to wage biological war upon the native people, led by Chief Pontiac near Pittsburgh. The deaths caused by this, now classified war crime, are said to be about 100. None of that is in dispute.
However, a second claim, that the Small Pox Epidemic of 18:37-1838, that wiped out tens of thousands of native peoples in North Dakota, was caused by US Army doctors ordering infected blankets from St Louis to be used to perpetrate a genocide upon the native peoples. This claim has been determined to be fabricated by Ward L. Churchill. The actual pandemic was caused by a steam boat, called the St. Peter, infected with Small Pox, that stopped at Fort Clark, North Dakota. And as a sidebar, the Federal government had not and did not take effective action to address the vulnerability of native peoples.