Wendigo
CaeIeste
It's not Walmart's fault that said person bought the gun.
If Wal*Mart sells somebody a gun, then yes it is Wal*Mart's fault that they have a gun. Wal*Mart would be instrumental to the process.
Walmart would not be an accessory to said crime because it's a chain of stores; not a person / thing letting it happen. That's like saying "I got a heart attack because I had some ice cream I bought from coldstone." Coldstone wouldn't be the issue here; because yes said person should know that buying and eating ice cream could potentaially be dangerous for them. It's not Coldstone's fault they create things with high sugar and calorie levels; it's the person's mind making the decisions. Therefore coldstone would not be an accessory to that person's heart attack.
It's all about how humans process the thoughts that come through their head. You're liable for the damage that you cause; even if perhaps you were sold a sledgehammer from walmart and that's what you used to cause significant damage to someone's property or person. It's not Walmart's fault that you decided to hit poor Sally with a sledgehammer because you happened to have bought it from walmart. Guns, like sledgehammers, have practical uses as well as it's negativity. I personally shoot skeet and trap as a club sport; and I'd like to go hunting as it is something my family has done for generations. Practical uses get overlooked when people decide they want to ban guns.
On top of all of this gun laws wouldn't really help all that much when it comes to gangs.
neutral
Since you would probably need several guns to hold onto what power you have I foresee people illegally purchasing guns from dealers across the border in places like Canada or Mexico. (Not saying they're bad; they're the only countries the US borders lol) On top of that guns would become an increasingly large black market trade. It's already huge; and having a ban on them would end up like how prohibition was with the speakeasies and such. The more people are kept away from something, the more curious they get. The more curious they get, the more they want it.