I think another important point to bring up about this is that people in large crowds or "mobs" often do things they would not normally do if they were alone or with a few people. When others are pressured to do something that the "crowd" is doing, it puts tremendous pressure on the others and sometimes forces them to simply go with the "crowd" instead of really thinking about what they are doing. Also, the lottery had been a ritual for so long in the town that many simply became so used to it and believed that the lottery brought them a good harvest. People had become so numb to the inhumanity and cruelty of it that they could not see the "light."
This story really does have a lot to sayabout how mobs do not react the same as individuals.
"group behavior tends to be more extreme than the typical behavior of its individual members" (Cornell University/mob_psych_MEP.doc).
This is a good description of this group. Individually, these are nice people. Mr. Summers runs the square dances, the young man is nervous about drawing for the first time, Janey is encouraged by the crowd. However, the small natural cruelties of human beings (boys collecting stones, Tesse's husband telling her to shut up, Tesse trying to pull her daughter and son-in-law in with them) are all exaggerated until the huge cruelty of the stoning seems normal... they even teach Davey with a few pebbles pressed into his hand.
First of all, the mindset of the townspeople is extreme conservatism, in a basic sense. They submit to the Lottery because their ancestors did. It had always been done. In a sense, it's a tradition.
Also, they saw some economic benefit in it. Without it, there was no assurance that crops would grow. It was purely self-interest in this respect.
They were aware that other communities had altered their practice of the Lottery, but as a whole, were not willing to alter their own.
And at the most elemental level, violence breeds violence. They wer caught up in the mass hysteria of the stoning. It gave them a sense of participation in the community and in insuring the community's survival.