In the first place, are those laws enforced? NYC has a law mandating a year in prison for illegal gun possession (or is it an extra year for crime committed with a gun? or both? anyway, they don't enforce it. they can't -- there are too many illegal guns for the number of prison cells. I'd say in the case of the Arkansas (Missouri?) kid who stole his grandpa's gun and killed some classmates that the grandpa 'screwed up a little.' Didn't read he went to jail even overnight -- am i wrong?
Second, putting someone in jail for five years after their kid has killed his best friend horsing around, or after the gunowner has killed his family, or someone has stolen the gun (does that count as a "little screwup"?) doesn't remedy the gun violence problem. Because the violence has already been committed. the victims are dead, and often the perpetrator too.
You seem to be making an argument I wouldn't normally associate with you (to the extent I am familiar through this list with your views). that heavy punishment is okay for what you regard as small crimes, and that punishment deters. Heavy penalties are just as much an extension of the power of the state --more maybe -- as the state regulating possession in the first place.