The left/right axis of the body is used in English to express several related ideas: comparison, judgment, equality, justice. It is also important to the center/side contrast.
1) Comparison, choice and judgment between things, as when we say "On the one hand,... but on the other hand..." Because our two hands are both similar and different, this phrase can express either similarity or difference, or both simultaneously. The hands are a clear instance of the body's bilateral symetry. The top/bottom contrast and the front/back contrast, however, indicate more difference than similarity and are thus of a different order. The two sides of an argument. Judgment, as in deciding between two alternatives. Sometimes we must "come down on one side or the other," but other times we can find a middle ground, a happy medium.
Justice and fairness are often expressed by an imaginary scale represented by the left-right axis of the body. Many statues or other symbols of justice use the scale with two plates suspended from a horizontal bar.
Despite the difference between the front and back of the body, the front/back axis can be used in a way that is quite similiar to the way we use the left/right axis. Two examples are the see-saw and the playing field: levelness represents fairness or a good relationship, and people move forward and back along their length to create a balance. "Meeting someone half way" on the "middle ground." A tilt of this axis is suggested by the phrases "one up," "putting someone down" and having the "upper hand," which express (possibly unfair) advantage or control.
2) Equality in mathematics is often expressed by showing quantities on either side of an equals sign (=) which is described as a fulcrum. The numbers on either side have to balance like a scale. The image of the scale is important because it represents fair measurement in economic transactions. These ideas are instances of a more general notion, equilibrium, meaning a sustained good relationship between two or more factors.
3) A range of possibilities is frequently pictured as spread out before us on a left/right axis. The most dissimilar items may be at the far ends, while things that closely resemble each other may be in the center.
The center/side contrast.
Things to the side are often less important and receive less attention than those in the center. Standard phrases: "a side issue," "a side order," "a side benefit," "a side show," and "I set it aside for more important things." This contrast, when put in terms of a circle or other area, is the contrast between center and periphery. The center suggests power, importance and moderation between extremes (centrists, the middle ground). It also is a way to talk about mental health, balance and calmness - being "centered," as if one found a "center of gravity." The periphery evokes people who are pushed aside, sidelined or politically marginalized, and who may be extremists.
Because the right hand is usually more agile and precise than the left, the left/right contrast has become a metaphor for suspicion and preference, as in "sinister" and "seated at the right hand." Because of the arrangement of political parties in the French Assembly during the 19th Century, the left/right axis has been used arbirarily to describe political contrasts and points of view.