What are 2 rules that are positive in their nature, and how do they help the community; also, what are 2 rules that are negative and questionable? Why, then, are rules and laws necessary in The Giver?

The rules of the dystopian society of The Giver are meant to keep life controlled and predictable so that life will be made easier and safer. 
Here are two rules that are positive in nature. These rules are not as restrictive as many of the others, and are, therefore, not so damaging to individuality:
1. "The evening telling of feelings" with the family (Chapter One)Whereas many feelings are controlled and certain words are not permissible, the discussion of emotions with one's family provides the members of a family a time in which they are relaxed together and share their thoughts and feelings. Even though they are restricted from using words that are considered too harsh or strong in feeling, the family members, at least, are in the safety of their own home. There they need not be embarrassed, as they often are otherwise if they say something that is not within the parameters drawn by their controlled society.2. The morning "ritual" of telling of dreams (Chapter Five)Again, because the expression of certain feelings are controlled through vocabulary and pills (e.g. "stirrings"), when the family members discuss their dreams, there is some outlet for individual expression. After all, much of the meaning that people find in their lives comes from the sharing of emotions and ideas. In addition, when they are out in the community, people must control themselves so much that they need outlets for voicing their feelings such as the family discussions.  
Here are two rules that have negative aspects:These rules are extremely restrictive and even deny people's humanity.
1. Assignments
That the Elders assign what role in the community each person will play is a denial of personal freedom of choice. This custom is extremely oppressive and denies individuality and personal expression. Each person should have the right to pursue whatever goals in life he or she desires. The Assignments handed out by the Elder are like receiving a life sentence from a judge except for not being considered a punishment.
2. The pills for "stirrings"
This rule also denies the humanity of the individual. In the community people are essentially neutered and are not permitted to procreate. To deny people their sexual feelings and the ability to have physical relationships and give birth to their own children is to deprive them of their essential natures.
The need for rules and laws
While no civilized society can be without rules and laws, these regulatory restrictions are usually made to protect citizens from those who would do harm were it not for such rules and laws. They are not designed to overly-control and restrict lives as is the case in the society of The Giver.