One other argument that I picked up here on TFL* is this: There's a difference between those rights that I, personally, need, and those which society needs for me to have. The prime example that I have used with this is our 4th, 5th, and 8th Amendment rights. I have never needed to move to exclude evidence in a criminal trial because my house was searched without a warrant and in an unreasonable manner (A4). Nor have I ever, personally, needed to invoke my A5 right against being compelled to testify against myself (A5). Nor has torture ever been used against me, personally, to get the aforementioned confession. Thus, I have never, personally, needed my Fourth, Fifth, or Eighth Amendment rights. As a society, however, we need to keep those in place. Without them, it becomes perfectly permissible for police to kick in doors, and torture confessions out of whomever they find there.
In my Walter Mitty moments, I imagine the conversation with an anti-gunner going like this:
AG: Nobody needs 30 rounds.
Spats: Has your house ever been searched without a warrant?
AG: No, of course not!
Spats: Then you've never needed your Fourth Amendment rights, have you.
AG: Umm, no.
Spats: Good. We'll just do away with that pesky A4.
AG: Wait!
. . . .
*= I truly wish I had articulated this before I saw it here, but, alas, cannot claim credit.