According to Mond in "Brave New World", why can’t man be independent?
Near the end of "Brave New World," in chapter 17, Mustapha Mond gives quite a detailed and fascinating dissertation to John the "Savage," explaining the reasoning behind the society that has been created for all "civilized" folks in the world. He discusses how mankind doesn't need God or religion, how knowledge is dangerous, and how productive citizens are programmed to be happy, content, and keep their place in the world.
One of the reasons that Mond gives for why mankind should not be independent is that because if they are independent, if they do think for themselves, then they become restless and cause chaos in society. They, as he puts it,
"would upset the whole social order if [they] started doing things on their own."
If they are left to choose how to do things independently, making their own choices about what they thought was the best way to expend their energy in society, then "social order" would be lost. Society would be dynamic, volatile, and exist outside of "controllable" possibilities. This, for a government craving ultimate power and production, is trouble. So, to keep people in their society from being independent, and from having the power to make their own choices, they program them from conception to think certain thoughts, crave certain things, perform at a certain level, and behave in certain ways. They make sure that a lot of soma is available to become dependent on for an escape from any potential woes, and provide all of the necessary distractions that keep them from being alone and ponderous. They encourage group activities, refusing to endorse solitary pursuits that might lead to being able to be on one's own and be happy. All of these things foster human beings that are completely dependent upon their programming and society to dictate their behavior and thoughts. No rebellion, no individuality, no uniqueness or individual expression. And this, according to Mond, creates the wonderful, blissful existence in which he plays such a large role.
I hope that those thoughts helped a bit; good luck!
You might also want to consider their own formula: "When the individual feels, the community reels." When a "citizen" becomes an individual rather than just another cog in the social wheel, what they experience, independent rather than programmed, though makes them an unstabilizing influence in the society. Independent feeling/thinking is such a threat to social stability that these people are exiled to an island. We see what happens when a group of individuals are allowed to exit together ... total chaos and war. (It is also suggested that the "Nine Years War" was caused by excessive self-interest/individuality of social groups/states.)
Musta Mond's question position may be summed up in a familiar dilemma:
You can be free, but not happy; you can be happy, but not free.
Which would you select?