This regulation doesn't prevent any person who is known to have one of the listed conditions from purchasing a firearm. It prevents people who are so incapacitated by their mental illness that they are unable to work and deemed unfit to manage their own public assistance benefits for them from buying firearms. It also allows them to appeal and show that they are not a danger. While I respect the right of people to own firearms, I think it's OK for someone with severe mental illness to need to jump through a few extra hoops to be allowed to buy a gun.