"...with no other weapon is he likely to have created such a tragedy"

Tell that to the relatives of the 52 murdered (and 700 injured) by religious madmen in London on July 7th 2005, using explosives made primarily with common household ingredients. Other religious madmen attempted the same two weeks later ("allegedly"). Previously, in 1999, a political madman killed three and wounded 70 with a nail-bomb attack on a pub in London. All these mass killings (and "allegedly" attempted mass killings) occured in the UK after virtually all guns were banned here after the appalling outrage in Dunblane in 1996.

Whatever the merits or demerits of gun ownership by private citizens, these have no bearing on the desire and ability of homicidal maniacs to perpetrate mass murder.