Constitutionally, Psychosword, "arms" specifcally refers to "weapons". A machete is not inherently a weapon, it is a tool, as "Hispanic community leaders" point out. Using a tool that was designed to cut sugarcane to instead win in gangfights should be just as illegal as carrying a chainsaw to fend off attackers.
It becomes a question of intent. The intent of the thugs in carrying the machete is to do harm, not to cut sugarcane, and as such, they have violated the essence of the tool. The intent of a law-abiding citizen to carry a gun is quite different than the intent of, say, a hitman from carrying the same weapon. Any tool used in the commission of a crime becomes an agent of the crime. You can be indicted for armed robbery if all you have is a sharpened pencil, if the victim hands over their money because they fear you using the pencil in a harmful way.
Since thugs in Boston will never intend to cut sugarcane with their machetes, then there is no logical reason to carry one except to use the tool for an unintended purpose, in this case, gang activity. LEO's should be given the power to arrest any and all individuals carrying machetes who are not directly engaged in an activity reflecting the machete's original intended purpose.
I'm not saying to criminalize a tool -- just to criminalize the unlawful possession and usage of such a tool to a greater degree.