The population that we Americans most often hear need to learn to sleep in "their own bed" is young - our most needy and vulnerable citizens, our infants and small children.
We are encouraged to train them to sleep alone while we seek the comfort of our mate's warm body. We are told by large federal agencies (erroneously and with the back up of only psuedo-science) that it is dangerous to sleep with our babies.
Well-done research showing the benefits of co-sleeping with infants goes ignored. Historically SIDS was called "cot death" for a reason, it happens more often when an infant sleeps alone, in a cot! We are sanctioned by doctors, popular press and now the Consumer Product Safety Commission to encourage our children's independence just when they need us the most.
A baby who "needs" his parents is felt to be a problem. Poor baby.... as part of the animal kingdom humans are born so immature that they can do little for themselves. We are more like Kangaros without a pouch than deer. Our large brain and upright, 2 legged posture forced an evolutionary choice so we have a foreshortened gestation. During infancy a baby should be kept close to his parents, day and night. Our infants need at least a year before they can begin to take the first steps toward independence. They can't even walk or find food but they should sleep alone? We are one screwed up society.