You will need to find your own reasons why you feel the community adopts the policy of sameness. Readers may interpret the story and the actions of the elders in following that policy in different ways. Some will say Jonas's community is good because it provides a stable and comfortable lifestyle for all its residents; others will say the community is bad because it destroys any opportunity for individual self-expression.
''Sameness" reflects the efforts of the community members to create a society in which all citizens enjoy equality in all things. All residents are cared for by others within the community - infants by those whose job it is to be a nurturer, children by the man and woman to whom they have been given to create a family unit, the elderly by children who help out in the senior living facilities. All are assigned work based upon the abilities and interests they exhibit as youth. All are provided with food, clothing, shelter and transportation to give them the ability to function as contributing members of the community.
All are also controlled so as to be conforming members of the society. Language is expected to be exact and based on observable facts, with no unverifiable emotions allowed. Medication is routinely given, starting when an individual reaches adolescence, to suppress unacceptable thoughts and dreams. In the name of sameness, originality of thought or action is actively discouraged.
Sameness can come in a few different forms. My examples would be colour blindness, the community being geographically contained, and the way of life.
Colour blindness is 'mastered' in the community because the limited range of colours that the people in the community can perceive limits their choices, and choices would mean differences. It also increases uniformity and Sameness in the appearance of the colour of skin.
The community being geographically contained is another form of Sameness. In this case, climate control. This is necessary because during times like rainy seasons, transportation is difficult. Climate control is also found to be necessary for the community as the unpredictabel weather like snow made growing food difficult and it limited agricultural periods.
Finally, the way of the life of the people in the community would reflect on Sameness. The people have limited choices and are unaware of alternatives. There is no room for mistakes, and in other words, no room for choices. For instance, people in the community are only allowed to apply for spouses where they are carefully matched according to their interests and personalities. Happiness isn't important in the community, efficiency is. Also, decisions are carefully made by the committee of elders so that no wrong choices are made.