We know some things for sure:
1. There is a direct relationship between gun related deaths (murder, accident and suicide) and the number of guns in society.
2. The USA has a much higher death rate by guns than the average across all developed countries.
3. Guns are capable of killing more people, more quickly than other methods available to ordinary citizens.
4. Mass murder by shooting is a recurrent problem in several societies.
5. It's inarguable that reducing the number of guns in a population would reduce the number of deaths by guns.
6. It's counter-intuitive that reducing the number of guns in society would not also reduce the overall number of violent deaths and where it has been done with real intent (such as Australia after their mass murder) it has had very positive results.
The arguments for not reducing the number of guns in any modern democratic, society are strange and unique to the USA. They're a puzzle to other developed countries being a result of their frontier psyche, relatively recent revolutionary history and more than usually violent culture.
Life, don't talk to me about life - Marvin the Paranoid Android