Why do you think the village needs a scapegoat in "The Lottery" by Shirley Jackson?

While the lottery itself might have originated as a type of harvest ritual wherein the villagers engaging in human sacrifice were rewarded with better crop yields or a longer rainy season; it is clear that by the era in which the story takes place the ritual of the lottery has eclipsed its original meaning. The villagers kill Mrs. Hutchinson without knowing why they do, only that they must. The argument can be made that Shirley Jackson's "The Lottery" functions as a condemnation of fascism, of the inertia and banality of evil particularly given the publication of this story in 1948, so shortly after the horrors of WWII. The villagers give no thought to right or wrong, whether tradition and authority figures are leading them down the right path or not. They are easily lead into committing evil acts, as a hive mind without one dissenting voice to argue that the lottery is morally wrong. Even Mrs. Hutchinson does not debate the morality of the lottery, her protests are purely selfish and dedicated to saving her life and that of her immediate family (you will note that she tried to draw her daughter and son-in-law into the second round of the lottery).

I think the village still needs a scapegoat because they are keeping up old and archaic traditions for the sake of tradition. The story hints at an original reason for the lottery. Mr. Adams is talking to Old Man Warner about other villages starting to give up the tradition of the lottery. Old Man Warner scoffs at the idea, saying he thinks those other villages are full of crazy fools. Old Man Warner then mentions a little phrase about the possible origins of the lottery: "Used to be a saying about 'Lottery in June, corn be heavy soon.'"
It seems the original lottery needed a sacrificial scapegoat in order to secure better crops. A person would be sacrificed and killed by a public stoning. The people probably believed this led to a good rainy season, which would lead to a good crop harvest in the fall.  
Based on my understanding of the story, Old Man Warner is the only person who still remembers that phrase. That tells me the stated purpose of the lottery is not for securing better crops. The people need a scapegoat because that's all they remember needing.