You are absolutely right...the Founders never even thought of the ball point pen, internet, printing press, typewriter, radio, tv, movies, etc...as freedom of speech...so lets restrict those too!
...this is too easy...
Why would you want to indiscriminately throw 200+ rounds/minute around? I say 'indiscriminately' because if you have ever fired a fully automatic weapon; you would know that after the first 5-10 rounds leave the rifle, you have little control over where the rest of the clip goes.
Contrast this against your 9mm, .357, .45, .22 ect. One shot, and you have a really good idea where that bullet went. And with semi-automatics; we still have idiots spraying the neighborhood with bullets. Now, instead of maybe having 2-5 people getting sprayed in a crowd; the entire crowd can be cut in half.
Restricting purely offensive weaponry such as machine guns protects society as a whole, which is probably pretty close to the origonal intent of the founding fathers. I wonder how the founding fathers would felt about farmers with cannon?
I'm glad you're convincing yourself with your arguments, but they haven't convinced me. If you can come up with an argument why the Founders would oppose radio, for instance, make it.