There's little doubt that the ritual Aztec sacrifice contributed to the fall of the Aztec Empire, and in more ways than one. First, killing thousands of people, whether you or your neighbours, simply can't be good for a society. The loss of people in a loss that can't be calculated. Who knows how it would have been different if these people and their children had swelled the ranks that fought the Spanish, not to mention the other contributions they would have made.