Has anyone else wondered about the huge number of large-scale violent crimes done by nut-jobs on the U.S.?

Crimes that leave many dead or injured; crimes that are usually marked by significant weaponry? Crimes that are not part of a terrorist political or religious agenda or guerrilla war, nor are they for personal gain. Like the killings at the theaters at the Batman opening last night, or the Columbine killings, or the incident of the postal worker shooting up his former office [and adding to the English language “going postal”]?

Does it seem to have any connection to the American emphasis on the rights of the individual or on the American right to bear arms? How many other countries have “the right to bear arms’?