Sacrificing was a major part of the society because they were obligated to keep everyone of thier gods happy. The reason they had to keep thier gods happy was because if they did not the gods would upset the balance of Earth or completely destroy it.
To be sacrificed was a major honor. The reason they made it an honor was because they needed volunteers. The volunteers were needed because if they did not they would not have anyone to sacrifice.
Although, most of the people sacrificed were prisioners of war and slaves.