Having spent the majority of my time the last two days perusing the Amici Curiae briefs submitted in McDonald v Chicago. I have noticed an extreme difference in the "groups" filing said documents.
Those that support McDonald seem to carry a great deal of clout in the area of what is and isn't part of the constitution, what with groups as diverse as a bi-partisan majority of Congress, Attorneys General for 38 states and one from State Legislators. Included are a host of independent groups as diverse as the CATO Institute and the National Shooting Sports Foundation. Most of these organizations have dedicated a substantial portion of their existence to the Constitution and its guarantees.
Those that support Chicago, well, not so much. You can check out the differing opinions and read all the briefs as well as news reports here.