People, including dealers, are at liberty not to sell guns to people whom they don't trust, but it's an economic thing as well as a liberty one, so the Bill of Rights ends up applying to idiots too.
Rust and bureaucrats. Freedom and vigilance. Front sight and trigger. Kindness and firepower. Situational awareness and tolerance. Safety and concealment. Taxes and allegiance. Love of man and surgical marksmanship. Once a soldier, always a soldier.