I have a few thoughts about the line "nobody's going to take away your guns.
1) It's patronizing, and I think it's supposed to be. As the OP noted, "The tone of the statement is always that of the reasonable but exasperated parent (them) explaining something incredibly simple and obvious to the slightly backward and petulant child (us)." I think the listener is supposed to come away with the feeling that gun owners need to be dealt with as slightly backward and petulant children, and that the speaker of the line is the better-knowing parent.
2) As long as something short of "jack-booted thugs kicking in doors" is going on, it allows the speaker to say, "See? I told you they're not taking away your guns." Example: 3,000% tax on ammo, primer, and bullets? That's not "taking away guns." That's just a tax. Full firearms registration? That's not "taking away guns." It will allow the speaker of the line to be technically right in the face of an innumerable other acts that were, in and of themselves, wrong to begin with.
3) It's not just a lie, it's a big lie. It's a whopper. The anti-gun groups will work by small increments, but make no mistake as to what they want. They want the bulk of private ownership of firearms outlawed. (I say "the bulk" because even the most ardent anti-gunners would allow a few elite civilians to keep their guns, IMO.)
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.