This seems a bit over the top to me. I doubt the gun owners will resist with physical force. Maybe I'm wrong.
All that over a Marlin .22?
And an AR-7. A high capacity ammunition feeding device on one of those is kind of a moot point, since they rarely fire two rounds in a row without jamming (the ones I've handled anyway).
I agree that it's over the top, and I don't think you're wrong. For all of the anonymous, "They'll have to carry me out in a body bag before I comply!" posts one sees on the internet, the fact remains that rather draconian gun control laws have been passed in a number of states, and we have yet to see a rash of "Unintended Consequences"-style resistance. The vast majority of gun owners have either complied with such laws or quietly ignored them while hoping to fly under the radar.
Heck, I'll give a personal example. Here in Colorado, a law was passed earlier this year that outlaws the sale or transfer of magazines that hold more than 15 rounds (8 rounds if it's a shotgun mag). Magazines possessed before the law took effect on June 1st are still legal, though. My response? Buy a thousand dollars worth of normal capacity magazines, some for firearms I don't even own (but plan to later). I'm in full compliance with the law.
Now, if a letter such as the one above was sent to me demanding that I either sell my mags/guns or turn them in, what would I do? It's extraordinarily easy to be a keyboard commando and say that you're going to fire the first shot at Fort Sumter in Civil War: The Sequel, but when the feces strikes the rotating airfoil...it's a bit different, isn't it? Especially when you look around and don't see anyone else resisting.