Suicides involving firearms are fatal 85% of the time, pills less than 3%.

[Orrex]

49. Do retailers maintain records of who purchases which guns? For how long?

Why is this information not nationalized? What could possibly be the benefit?

No - not in the US legal system
if someone steals my car and runs you over, I am not responsible. If I can show I meet all legal storage requirements, I am not responsible for anything a criminal does if he steals my guns.

You asked what would be different if we had a national gun registry. Your objections are not consistent with your question because are based on the current inadequate system rather than on the system that I propose.

Under that proposed system, if a gun that is registered to you is used in a crime, then either:
1. You let the criminal borrow your gun, in which case you are responsible.
2. You sold the gun to the criminal without having it re-registered, in which case you are responsible for the illegal sale, which would be a felony, at least
3. The gun was stolen and you failed to report it, which would be a felony, at least
4. The gun was stolen and you reported it, in which case you may or may not be liable depending on the circumstance of the reported theft (e.g., did you leave it in the back of your pickup or was it secured in your gun safe?)

The law that I am proposing would legally require responsible gun ownership. In contrast, you are claiming that a Gun Owner's Card will magically reduce or stop gun violence.

Since you're so quick to point to the millions of existing firearms as the reason that it's absurd even to suggest the possibility of a gun registry, then what in the world would your magic Gun Owner's Card to about them?