In Mockingjay, the rebel propos were used to both recruit people and create a rallying of supporters in Panem. In some cases, they were used as distractions, such as in the rescuing of Peeta.
Answer: The purpose of the rebel propos in the Hunger Games: Mockingjay is that they communicated messages to Panem's citizens, giving statements against the Capitol, and provided a rallying point for the rebel war effort. The propos in Mockingjay are significant because they were propaganda and distractions for a rescue mission. They were entertainment as well.
A bias is a favor of a side or opinion others may not agree with, so this statement is a common bias, that parents say because they are in favor of kids learning to help others.