In the US, there are more firearms than people. About one-third of all households have at least one firearm [0]. The vast majority of these people have never had a serious brush with law enforcement, but some significant portion would refuse to part with their guns if a ban were enacted tomorrow. While it is said that nearly all Americans are felons [1], most Americans do not intentionally commit felonies or think of themselves as being on the opposite side of things from law enforcement. That would suddenly change for millions of ban-defying US citizens, and it's hard for me to imagine a likely scenario where that decreases violence in the US.
[0] https://www.npr.org/2016/01/05/462017461/guns-in-america-by-... [1] https://ips-dc.org/three-felonies-day/