There is a benefit to banning assault weapons or whatever you want to call them. Weapons that can kill everyone in a cafe or church or classroom or parade or cinema before they can flee. If you force people to go to the black market for mass shooting weapons it will make it harder for teenagers and mentally ill people to get them as they don't have contacts in the black market. The last two US school mass shootings involved an 18 year old walking into a gun store and legally buying an AR-15 and hundreds of rounds of ammunition - they had school shooter starter kits on sale.