You are focused upon a legal definition of the word, firearm. Most folks do not draw a distinction between that and common perception of a firearm is. The legal definition can vary from jurisdiction to jurisdiction.
For example, my repro '61 Springfield is defined as an antique under the U.S. Code which means it is an exception to the definition of firearm for that particular chapter of the code. My repro is similarly defined and exempted in the Revised Code of Washington. However, the Seattle Municipal Code uses a more common definition of firearm. Actually, the muni code is ambiguous because it does not distinguish between rimfire and nonrimfire weapons. When I and my pards would hike in one of the city's largest parks in preparation for campaign events back east, we have been visited twice by the local cops after parks people got nervous about people with GUNS hiking the trails. Since I have met many officers in my occupation, there's never been any real problem. However, we got tired of being stopped by cops and park staff so we ceased marching in Seattle parks. Tacoma has similar provisions in its parks code, but we don't get hassled there. Same goes for the state and national parks because we don't get hassled there, either.
I also agree that the sky isn't falling. This is something which has made the press and is the typical man bites dog story. From my experience with the press, they usually bend the facts all out of shape by adding a dose of sensation. It's called a story for a reason.
A little regulation which includes some gun safety wouldn't be such a bad thing. Some reenactors I've seen on the line really scare me. I'm not just thinking about the fresh fish attending their first reenactment. Some folks who have been around a few years would do their file partners a huge favor by spending a little quality time reading and walking through the procedures for loading and firing from the manuals as opposed to repeating what they've always done.
"While the original battle [Gettysburg] may arguably be considered the epicenter of the history of the war, the GAC reenactment is not the epicenter of the hobby. To confuse or equate the two is unfortunate. - Bernard Biederman, 6 July 2012
"Authenticity conflicts occur when reenactors from one end of the spectrum attend events at the other end of the spectrum then try to impose their own standards instead of event standards."