[The_Reader_David]

Actually, the set is not empty, but has three elements, each involving preventing access to firearms by a circumscribe group of people: convicted violent felons, the psychotic, and unsupervised children.

[NorthMountain]

1) Convicted violent felons are already prohibited by law from possessing firearms. Therefore, such prohibition is no longer a matter of legitimate advocacy.

2) Psychotic? Sez who? Have you ever filled out a Form 4473? Gun control advocates' concerns about mental health are illegitimate, as their advocacy is aimed at harassing the honest, sane gun-owner.

3) Unsupervised children? Have you ever filled out a Form 4473? Gun control advocates' concern is again illegitimate, as their activities are again aimed at harassing the honest, sane gun owner.

No, sir.

"[T]he legitimate concerns of gun-control advocates" is the empty set.