In principal I agree. But as we can see in the US, even when they can't prevent you from buying the gun they can still limit the ammo. Serializing ammo, making companies go out of business, import restrictions, etc. Even those who reload need to buy the primers. Granted, if there are a trillion rounds in circulation already then that is a shitload of hoarded ammo out there – for some of us.
With an energy weapon or coil gun there is no way they could regulate or bottleneck the ammo. Attempts to bottleneck the parts would be very difficult for them, since they would be commercially available components like capacitors. In a way, their incessant push for 'lower carbon' is pushing battery technology way farther than would have been the case ten years ago. Countries without access to guns still have hobbyists and machinists who can build shit. So the emergence of this kind of weapon would be a tremendous equalizer. Govts no longer able to limit arms, except by punishing those caught in posession.
There will always be the delusional set who want to regulate knives and any form of threatening weapon, so what we are discussing would certainly end up being considered black market. No way of getting around this aspect of it, no matter what we do. As you indicate, they are coming for you (us).