Obesity is the result of a loss of self-control. Indeed, loss of self-control might be said to be the defining social (or anti-social) characteristic of our age: public drunkenness, excessive gambling, promiscuity and common-or-garden rudeness are all examples of our collective loss of self-control.
How many people does each of us know who claim to seek happiness but freely choose paths inevitably leading to misery?
Childhood in large parts of modern Britain, at any rate, has been replaced by premature adulthood, or rather adolescence. Children grow up very fast but not very far. That is why it is possible for 14 year olds now to establish friendships with 26 year olds - because they know by the age of 14 all they are ever going to know.
Life is a biography, not a series of disconnected moments, more or less pleasurable but increasingly tedious and unsatisfying unless one imposes a purposive pattern upon them.
The idea that man is a tabula rasa, or Mao's sheet of blank paper upon which the most beautiful characters can be written, is an old one with disastrous implications. I do not think though that the cults you mention could survive honest thought about human nature.