in the past these people would have been executed wthin days or weeks of sentencing, for capital crimes. they would never have had a chance to own dangerous weapons and murder or’threaten murder, again.
so we either go back to executing people for heinous crimes so they cannot get out into society again, and terrorize people again, or they live, do their non-death sentences, and yes, cannot buy guns again.
the only caveat is that the restriction should fit the crime. if it was non violent crimes without weapons, this should not apply.
So an 18 year old should never be able to own a gun again if they lead a lawful life for 40 years?