Mill claims that people are persons if they are rational - and that their unique thoughts are what give people individuality. This does not include “barbarians,” children, delirious people etc. who, according to Mill, would require some representative or guardian to act for them. (This also has implications in the harm principle. = One can exert force onto a child to prevent them from from committing suicide for instance.)
Mill believes that conformity will lead to the downfall of Western civilization:
“Over himself, over his own body and mind, the individual is sovereign” “Customs are made for customary circumstances and customary characters; and his circumstance or his character my be uncustomary” “He who lets the world, or his portion of it, choose his plan of life for him, had no need of any other faculty than the ape -like one of imitation. He who choose his plan for himself, employs all his faculties. “Even despotism does not produce its worse effects, as long as individuality exists under it.”