A right for a citizen is a right. Only if you have been adjudicated properly as unworthy of exercising that fundamental right may it be infringed.
Felons? Infringed until rights formally restored.
Nuts? Infringed if adjudicated nuts. Restored if adjudicated sane.
Weird politics? Not infringed.
Terror watch list? Not infringed unless adjudicated or convicted of some crime, or found nuts.
Rights can only be taken away after irresponsible or criminal conduct. We don't subject newspapers to background checks or say they can only print so many copies. We don't guarantee jury trials on condition or social status.
As for what the line is on civilian arms --- I guess I draw the line at nukes or WMDs or gas -- weapons which are absolutely not defensive in nature.
