Guns are used for good quite regularly, it's just that prevented mass shootings and other prevented crimes don't get the same attention.
So when a mass shooting happens where the assailant is sadly not stopped and kills lots of people, you get the "hurr durr where's the good guy with a gun?" bs because people are not aware of incidents like this.
Good guys with guns defend themselves and stop crimes hundreds of thousands to millions of times a year. They just don't get a month of news coverage and a Bloomberg financed march.
https://www.forbes.com/sites/paulhs...ked-about-defensive-gun-uses/?sh=11aa30c1299a
Remember that this includes everything from killing an assailant, down to simply brandishing a gun to dissuade a potential attacker.
https://www.nap.edu/read/18319/chapter/3
The lowest end estimates are around 70,000 a year. Which is still 6-7x our gun homicides, and far more than all gun deaths.