Ah, you are looking for the universal element of this haunting story by Shirley Jackson. Through the lottery, Jackson shows us the natural acceptance of routine and ritual that pervade our lives. Because a tradition has always been carried out, we accept it without question, just as the citizens of Jackson's small town accept the tradition of the lottery. They do not question its morality because it has always been a part of their lives.
Perhaps traditions regarding segregation in our country could be compared to the lottery. Before the Civil Rights movement of the 1960s, many white people did not question the morality of having separate black and white schools, separate restrooms, restaurants that would serve only whites. This was the way things had always been, so this type of discrimination was so ingrained into our psyches that we did not question the unfairness of this situation.
There are probably many practices today that we accept that later others will see as barbaric and savage. Jackson asks us to examine more closely and more critically our own customs, practices, and routines.