Why do we celebrate Guy Fawkes night?

Guy Fawkes night is the annual commemoration of the foiling of the Gunpowder Plot - when 14 individuals planned to blow up the House of Lords during the State Opening of Parliament on 5 November 1605.

The BBC's Carol Kirkwood asked bonfire night organiser Graham Callister why we celebrate Guy Fawkes night when it was in fact a plot to maim and kill.