Well, this point may seem like a sidetrack but it is important to the select fire and even semi automatic weapons and their use in crime.
Like someone pointed out, there are not that many select fire weapons in common use because they have been essentially barred from common use for quite some time.
When I was in school as a criminal justice major, the stats actually don't show to either help or hurt us in terms of gun ownership and crime. Whether pro, or anti gun, the laws either way actually didn't show any correlation to the increase or decline in criminal activity.
Now, no one is stupid here, so we know the causes are larger issues such as education, ecomony, etc. etc. But mainly, the street violence and "public safety" issue that everyone is so concerned with is due almost entirely to legislation that is non gun related. My case in point here is the "war on drugs".
To make drugs relevant in our street crime and violence today, I'm going to go back to the 20s and 30s of Prohibition era America. This was pre machine gun tax and if it wasn't for the Volstead Act, there would have been virtually NO violence using machine guns or any other guns. But naturally, when you have stupid legislation that was impossible to enforce, you have an incredible entrepreneuring activity for the criminal element. And this is where the almost weekly violence in the streets of America stemmed from, over distillation and distribution rights, and turf wars, etc. of the gangsters and mobsters of the era which are now infamous through Hollywood and print media. So, again naturally, the stupidity of the public, and the elected officials placed the blame for this violence on the machine guns and we have our first anti gun legislation.
You know where I'm going next, fast forward to today. No firearms, automatic or otherwise would be a "problem" if it were not for the failure that is the "war on drugs". I place "problem" in quotes because with over 300 million guns in the US, and only 3000 some deaths a year (according to the Brady Center), those numbers turn out to be an insignificant percentage. So in reality, there is no problem at all. To further muddy the waters, the Brady Center does not help put things in context because they also don't say where the majority of this "gun violence", and harm "caused" by firearms is occurring, which is in the large metropolitan areas where the gangs are fighting over the same things their Irish, Italian, and Jewish counterparts (albeit they were classier breed of criminals) did in the 20s, turf control, distribution rights, except over drugs instead of alcohol.
Furthermore, these end users of firearms do not appreciate them like many members of this forum do. They don't care about history, or appreciate machinery. Thusly, they will not treat them in the responsible manner that many of us would. So, many of these "accidents" etc. from firearms is from irresponsible people to begin with, not to mention in homes where there is undoubtedly some form of criminal activity going on. This is also where the horrible tragedies involving children getting harmed by the guns come from as well, because logically, these wouldn't be the most responsible parents.
So, my point is, what kind of weapon it is, is really irrelevant to a public safety conern, because there isn't much of a public safety concern. Not to mention, that practically, a semi auto rifle or "SMG" when used in a disciplined manner isn't any less dangerous than its select fire military cousin, and we already have millions of them around, but a very small percentage of crime using firearms, are with these types of guns.
But all of this "sociology" is an aside from what is protected under the 2A, which the majority of you have already gone over. We all draw the line somewhere, but drawing the line to exclude machine guns is anathema to the meaning of the 2A.