The society has many structural guidelines because it is an attempt to build a utopia - that is, a perfect society - by controlling all natural human tendencies. The result is a soulless, totalitarian society.
Three major areas that totalitarian/utopian governments usually attempt to control are sex, family, and individual liberty. These three areas cause a lot of trouble in ordinary human society, so they are a natural target for anyone trying to build a utopia.
In The Giver, the instinct for sex/romantic love is suppressed with the use of pills. As soon as preteens or teens feel "the stirrings," as they are called (the beginning of interest in the opposite sex), they are to report them, and then they are given pills that suppress the stirrings.
Families are chosen by the leaders. Each family has a father, a mother, and children, but they are not biologically related to one another. Children are borne by birth mothers (also specially selected for that role), then assigned to families. "The Old" live not with their grown children (who would not really be theirs anyway), but in a special home for old people.
The idea that suppressing natural family bonds will lead to harmony in society is a very old one. Plato floated it in his Republic. In The Giver, putting this idea into practice leads to dull, grey, loveless "families." These families are not completely without affection, but the father and mother are not sexual partners, and the mothers did not actually give birth to the children they raise. Even asking about "love" is viewed as using "imprecise language."
Individual liberty is also basically nonexistent in the society of The Giver. Children are assigned a vocation - a lifetime career - when they turn 12, based on the leaders' observations of their gifts. They are assigned their family, their clothes, and so on. At the beginning of Chapter 13, Jonas expresses to The Giver the reason for this:
"We don't dare let people make choices of their own."
"Not safe?" The Giver suggested.
"Definitely not safe," said Jonas with certainty. What if they were allowed to choose their own mate? And chose wrong? Or what if," he went on, almost laughing at the absurdity, they chose their own jobs?"
"Frightening, isn't it?" The Giver said.
Jonas chuckled. "Very frightening. I can't even imagine it. We really have to protect people from wrong choices."
In the end, even life and death are controlled in the society of The Giver. Babies are euthanized if they don't gain weight fast enough (or are the smaller of a set of twins). It turns out that the quest to make things perfect for people often leads to killing quite a few of them.