What is often the first expression of latent discontent with an existing system, and is often considered the authentic voice of weaker or oppressed groups in society?

social movement

Explanation:

social movements are called as the first expression of latent discontent with the existing systems and the  

Social movements are known to be the original voice of oppressed or weaker groups in the community because they are not in a position or does not have a way to assemble themselves as an interest group so due to that they use such movements as a medium.

Though they lead to the generation of the interest groups that have particular or similar goals. These groups  hire the members by offering them incentives to be a part of that group.