Great Border Patrol

So if you can be detained for trying to bring a pair of nail clippers or a lighter on a plane, how come someone carrying a bloody chainsaw can waltz in through the U.S. / Canadian border without a hitch? Instapundit linked to this article from the Washington Post. I swear I don't know what country we live in anymore. Why don't we just put up signs at the borders that say, "Come in, make yourself at home and kill us."