Before the earth was created, there was a great council in Heaven. And our Heavenly Father presented a plan that would not only allow his spirit children a physical body and experience, but the ability to choose for himself whom and how they would serve. Of course, people wouldn't always choose good, and then they would not be able to come back to Heavenly Father. That is why Jesus was prepared to be our Savior. He would provide a way back for all those who made less then perfect choices at times (if they believe on him).
Satan, on the other hand, did not like a plan where people were allowed to fail. He offered a plan where he would make everyone do good and he would receive the glory for doing it.
We voted down Satan's plan, trusting in the Savior and understanding the wisdom and beauty of our agency.
This agency is so important to Heavenly Father that he allows us to even do bad things to other people. He allows murders, and other ugly things to happen in the world....just because agency, our ability to choose for ourselves, is such an important factor in the plan.
When others attempt to force something upon us, we often feel rebellious and we have every right to feel that way. We fought for agency. We are not going to let others take it away.