One of my mentors once said this to me - "If you went shopping with your children and told them to behave and do not touch the food in the produce aisle, their thoughts are on not touching the food, and human nature leads immature and rebellious children to do the very thing they are told not to do."
In the same way, signs that say keep off the grass, invite some to walk on the grass, or signs that say Do Not Enter - it invites immature and rebellious people to enter.
Even God Himself gave us the Ten Commandments knowing they would be broken by mankind - so that we would realize we could never keep them and see our need for a Savior.

Having a Gun Free Zone is like that. It will not bring lawfulness but rather, invites more unlawfulness. Just because Umpqua CC was not a gun free zone does not mean it needs to be one.