What is the issue, which Mill is dealing with?

Mill issue in On Liberty is just as the title reads; his issue is on "liberty." He writes of how liberty has positive effects on everyone, that all society benefits by it. Liberty allows people to progress and avoid social stagnation. Liberty of opinion is valuable for two main reasons. First, the unpopular opinion may be right. Second, if the opinion is wrong, refuting it will allow people to better understand their own opinions. Liberty of action is desirable for parallel reasons. The nonconformist may be correct, or she may have a way of life that best suits her needs, if not anybody else's. Additionally, these nonconformists challenge social complacency, and keep society from stagnating.