Does "The Lottery" suggest that people are innately violent or that their behaviour is learned?

Although the behavior to hold the lottery each year is learned, as part of the culture and tradition of this society, I would say that the people of the town are very violent.

Mrs. Delacroix, a friend of Tessie Hutchinson, who speaks to her when she arrives late for the lottery, is the person who tells Tessie to not be upset about her forgetfulness.  But then when the victim is chosen, Mrs. Delacroix picks up the heaviest stone, so heavy, that she can barely lift it.  This is a clear example of a violent tendency.

Additionally,  Bill Hutchinson yells at his wife for complaining about the selection process being rushed.

"When Tessie questions the method of drawing, he says, "Shut up, Tessie"; he also forces the slip of paper with the black spot on it out of her hand and holds it up in front of the crowd."  

This story is an expression of the dual nature of humanity.  The fact that individuals can be both good and evil at the same time.  The people of the town are eager and capable of murdering a member of their community with cruelty and indifference. Stoning is a violent way to die. 

There is one individual who feels repelled by the process, Mrs. Dunbar, she does not rush to stone Tessie. 

"Mrs. Dunbar had small stones in both hands," (Jackson)