Where there are many people, you don't need to care what people around you and outsiders think. Hubbub described the noise of the crowd as if it were boiling. The louder the noise, the more you have to listen to yourself. It means that in a crowded place, you don't need to care about the opinions of people around you and outsiders. To be yourself is to be loyal to yourself, to have personality, to have opinions and characteristics, and not to care what outsiders think.