What a perfectly meaningless thing to say.
By suddenly allowing something that is presently illegal, of course you are going to lower the crime rate. It wouldn't lower drug use incidence - it would just legalize it.
That isn't 'curbing crime' any more than 'not having money to eat' is 'curbing your appetite'.
The problem with existing gun laws in the US is that they are not nationwide.
In a land with uncontrolled inter-state borders, a law in State A has very little effect on State B; and since anyone in State B can walk in anytime they want to State A, it doesn't really affect much.
If you witness, however, countries with nation-wide gun restrictions, you see in every single case a lower incidence of gun violence.