The colonization of the new world was largely an immunological accident.

When meeting Europeans, 90% of the Americans would catch some European disease and die. This was widely seen as the will of god(s) by both sides. Often the disease spread faster than the Europeans, so when they got to an area most people were already dead.

The following conquest is seen as barbaric and unjust by us modern people. But for the people of the time, it was just how the world worked. The Aztecs would have been overjoyed to conquer Spain the same way.

You're right, but I think too that the Europeans happily took the deaths as an opportunity and justified it.