Why would the rebels want to kill every man, woman, and child in each village Ishmael has traveled to? Why would they kill them when they're innocent people who have done nothing wrong with the rebels?

They kill them to instil terror in the public. Once they have done that, they can easily manipulate and control the people. Many people are killed along ancient tribal lines and tribal affiliations. Finally,sadly, these rebels simply like raping and pillaging the towns and villages.

They instill terror.

They install terror in the villageranga

*Village