The alternation of left and right has what has kept our nation stronger and more stable than any other on the planet over our two centuries of one consistent Constitution:
Right:
Limitation of government
Respect for tradition
Fiscal responsibility
Strong military
Left
Fairness in economic matters
Welcoming posture to the world
Respect and concern for human rights
Concern for the working person, more than for the wealthy
Most historians will tell you if we did not have both, we would be in trouble.