First, you have to start somewhere. If one person legally purchased a nuclear bomb, I don’t think they shouldn’t pass a law preventing anyone else from purchasing a nuclear bomb.
Second, you’re not going to be carrying around any long gun. Those will be for home defence at most, likely just a range toy (and also to be shown during a protest to make sure other people know your people are armed). Maybe it’ll be useful if we end up in a civil war or something, idk. A handgun is nearly as good at killing people and can be carried around easily. If you want protection from these people then you want a handgun.