The biggest flaw in Brave New World is the suspension of disbelief that we will have developed the technology to control society to the extent that they do.
Brave New World is a dystopia where all of the people have accepted the possibility that every aspect of their society is controlled. We know that the book takes place in the future, because references to Shakespeare and Henry Ford are made. There is a reference to the year “A.F. 632” in chapter one. Henry Ford is deified, as the founder of the modern era, industrialization, and the assembly line. Henry Ford was born in 1863, and if we use Christian dating conventions with the year 0 being the year Christ was born and the year 0 being the year Henry Ford was born, the book would open in the year 2495 our time when the story opens. Brave New World was published in 1932.
Granted, a lot could happen in this amount of time. We have no way of knowing. We could have human cloning, complete social control, and a society that barely resembles our own in 481 years. The society in Brave New World is different from ours scientifically but also sociologically.
The main difference is that not only is there a strict class structure, but the classes are made up of genetically modified clones.
[The] Alphas and Betas remained until definitely bottled; while the Gammas, Deltas and Epsilons were brought out again, after only thirty-six hours, to undergo Bokanovsky's Process. (Ch. 1)
The “Bokanovsky's Process” is the process of human cloning. The Lower classes are clones, and the Alphas and Betas are the upper classes. They have more freedom. They are not all sterilized.
Employment, recreation, housing, and every aspect of a person’s life is dictated by class. Education of the lower classes is limited by their intelligence, which is in turn limited by where they were cloned from. They are reserved for labor and grunt work at the lowest classes, and even their clothes show what class they belong to.
Another way the society is completely different is the sociological aspects of family structure. Basically, there isn’t one. Because there are clones and humans are reproduced by genetic processes, there is no need for the nuclear family consisting of the mother, the father, and the children. This does not mean that there is no sex in Brave New World’s society—quite the opposite is true. Sex has become recreation. It is used from childhood on to make people feel good, and has become completely devoid of emotional connection.
"Our ancestors were so stupid and short-sighted that when the first reformers came along and offered to deliver them from those horrible emotions, they wouldn't have anything to do with them." (Ch. 1)
Like most dystopias and science fiction books, Brave New World requires quite a bit of suspension of disbelief, which is the idea that you have to accept the fictional world being described for the purpose of entertainment. If there is a flaw in the book, it is that the reader must accept that in a few short centuries, society will break down—or advance—to the point where all of this is possible.