Why does Jonas's society chose to institute sameness? What are some of the consequences on peoples' lives in this community?

Jonas's society decided to adopt the Sameness for a couple of reasons. The Sameness establishes a uniformity for everything. It's trying to make everything more or less equal, and that will hopefully eliminate discomfort, anger, unhappiness, etc. in society. The people also give up a fair amount of free will for the Sameness, and that wasn't seen as a bad thing. By removing a lot of choice, the people are less likely to make wrong decisions. You can't make a wrong decision if there is not a decision in the first place. Finally, the Sameness is a form of societal control.

"Our people made that choice, the choice to go to Sameness. Before my time, before the previous time, back and back and back. We relinquished color when we relinquished sunshine and did away with differences….We gained control of many things. But we had to let go of others."

The consequences of a society like this varies. The elimination of discomfort and anger sounds nice, but the opposite of those things was also relinquished. The people assume that they are happy because they can't feel sadness, but how can one truly know happiness if one doesn't know what sadness feels like? Jonas doesn't understand this concept until the Giver gives him truly joy filled memories like sledding down a hill and truly horrific memories of war. The more Jonas learns from the Giver, the more Jonas comes to believe that the Sameness is not good for the people. They can't choose anything, and they aren't really feeling anything.