The past is the past.  People from the 1500's on prioritized differently than in 2017.  Britain, France, Portugal and Spain were in the midst of a massive expansion of their empires and if one wishes to call it colonialism was a fact of life.  Spain completely wiped out the whole the Incan population and stole their wealth.  Portugal did the same in other parts of South America.  To say that the British were alone in these colonialist activities is ridiculous.  Survival at the time was to make your empire larger and not get swallowed up in the other country's expansion.

In this case Cornwallis was doing the bidding of the crown by establishing Nova Scotia with enterprise in the form of farming, fur trading, shipping,  forestry, factories, etc.  The MicMac were reacting negatively by raiding farmers and stealing the food they had grown.  Cornwallis reacted in a way that would not be acceptable today but by attacking villages and farmers the MicMac were declaring war on the British.