It's a mistake to assume that the legal definition of insanity used to determine whether a defendant can stand trial is the only one relevant to conversation.
Someone who commits mass murder can be legally sane if they are cognizant of the concept of right and wrong, are not severely mentally handicapped, are capable of understanding and responding to questions, etc. Yet I doubt anyone would consider a person capable of shooting up a synagogue to be sane. I don't think it would be "strange" to consider that someone with suicidal thoughts or someone in the heat of passion should be trusted with a firearm simply because they can also sign their own name.
Well the discussion was about "crazy" people, people who are not just colloquially crazy (ie Bob is crazy if he thinks we can get this fix done by the weekend) but clinically insane.
> someone with suicidal thoughts
I don't think someone with suicidal thoughts is crazy. In fact I've never heard of anyone that doesn't have suicidal thoughts at some point in their life. That's a normal part of human existence. Different from an attempted suicide though. And someone attempting suicide is also not insane simply because of that.
> or someone in the heat of passion
That doesn't sound like insanity to me either. I don't even know how something like that could be evaluated. How would a gun seller know someone is in the "heat of passion"? The phrasing suggests a temporary emotional state of some kind. Perhaps the idea is if they are ranting and screaming at the gun seller and claiming they are going to use the gun to commit a mass shooting. And in that case gun sellers don't sell guns. Someone who in this heat of passion who intends to commit violence presumably is going to act normal while buying the gun. Not insanity, not something that can be determined at point of sale.
> I doubt anyone would consider a person capable of shooting up a synagogue to be sane
Antisemitism is pretty common among those known to be sane. No physician would diagnose madness simply based on antisemitic beliefs. There have been groups in history that mass murdered Jews, and other groups, who were the predominant people and majority of their society. They were not insane in the general case so it's not correct that someone capable of committing atrocities, including genocide, is not sane.
Is a previous diagnoses of madness by a qualified medical professional using accepted standards of practice a common or even not-infrequent attribute of mass shooters and murders? Not that I can see. So we're back to someone not known to be insane - a sane person - doing this crime and the label only being applied after the fact.
Again, I propose that the insane are more responsible gun owners than the sane because so few murder convictions involve those actually determined at any point to be insane by anyone qualified to make such a determination. It's easy to say killers are crazy. How does that help prevent crime? It is counterproductive in fact because it suggests that restricting civil and constitutional rights of people with diagnosed mental illnesses (about 1/5 the US population is on psychiatric drugs which require a diagnosis to be prescribed) is a solution when this group is not in fact the group that is committing these crimes and therefore there is no reasonable premise for restricting said rights.
Someone who commits mass murder can be legally sane if they are cognizant of the concept of right and wrong, are not severely mentally handicapped, are capable of understanding and responding to questions, etc. Yet I doubt anyone would consider a person capable of shooting up a synagogue to be sane. I don't think it would be "strange" to consider that someone with suicidal thoughts or someone in the heat of passion should be trusted with a firearm simply because they can also sign their own name.