Why did the MOUNTAIN MAN BOOF Bobby in the monumental Blockbuster motion picture; "Deliverance?"?

The writer(s) needed to include a significant rape scene because it is symbolic, in that the movie depicts the rape of the land, as well. What happens to Bobby parallels what happens to the natural surroundings. The river valley is flooded by the construction of a dam and all those town folk will have to move. The setting is also in the Georgia wilderness, where the states most remote white-water river flows. That, too, will be lost after the dam is completed. There is a clash between the snobbish outsiders from the city and the native people of the rural area.

Because he looked damn good. Giggitty!