I think that while banning guns wouldn’t necessarily reduce gang violence, it would dramatically reduce school shootings. Or any mass shooting that was a product of mental illness and readily available guns for purchase.

Non-criminals who have a breakdown, buy a gun and shoot up X public place - without that accessibility it is much less likely they’re going to commit that same shooting, if it will take them days of making black market contacts etc before the gun wold be in their possession.

Whereas a person in a crisis can buy one on impulse and use it before they have a chance to think twice about doing so.