You may reject all of the rationales offered above, which is fine. It’s totally respectable for you to admit that you don’t believe the rationales for AR ownership outlined above are legitimate, and therefore we should outlaw civilian ownership of a very large category of weapons. But what isn’t respectable is to argue this way, and then to turn around and claim that “nobody is coming for your guns!” That’s insulting, and we both know it isn’t true. Stop doing that.
If you’re serious about banning guns, you can talk about banning all semi-automatic guns, or about restricting guns to a list of approved models or actions. This is may not be politically realistic at the moment, but at least it’s consistent and rational. But talk of banning just the “AR-15” — as if that’s a specific model of gun that you can just up and ban — is technologically infeasible and ultimately counter-productive.
So the “defensive rifle” (as opposed to the “assault rifle”) is a nonsense idea that exists only in the minds of people who know nothing about guns. This being the case, you can’t fault gun owners for not buying or building such a weapon, because that is not a real thing and never will be. An assault rifle is a defense rifle, and a defense rifle is an assault rifle; these two concepts are identical — such is the very nature of armed combat, in which one person is trying to prevent himself from being killed by killing the other guy first. Anyone who “needs” a defense rifle “needs” an assault rifle, because they are the same.