It is of course effective.He wants people to understand that".. giving freedom to human nature.." will cause conflicts but that is a human characteristic.
Mills rejects any type of coercion in peoples´opinions or in the way they act.Punishment should be inflicted only when the freedom of a human hurts his equals.When Mills expresses his points of view in the essay he convinces people that it is the right manner, there is no other fashion for living but that of being in liberty.
Mills chose the essay to convey his ideas because he wanted to be taken seriosly .He used the resource of rhetoric as it gave him the opportunity of making people reflect on what he wrote and ask themselves on the importance of acting freely.