Bob Jefferies, the selectman pushing this, openly admits that its purpose is political grandstanding, not anything relating to public safety.
Given the realities of enforcement (and I agree with a lot of the points calsdad is making -- to have meaning a law like this must employ a great deal of force), why not push supporters to admit they have no intention of enforcing this thing? Then offer to formalize their intentions. If they really just want to engage in grandstanding, suggest adding a sentence that says, "This bylaw (or whatever it is), intended as a symbolic gesture and statement of town feelings and concerns regarding guns, is not meant to be enforced, nor are stated penalties meant to be applied". If they don't like that, make them say exactly what they intend to do to enforce it, how they intend to handle those who ignore it, and what they are willing to spend to get all of this done.