The right to bear arms is the 2nd ammendment to the US constitution, so they can rise up and form a militia if they get upset about something:
Amendment 2 - Right to Bear Arms. Ratified 12/15/1791. Note
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
Sadly, the right bear arms isn't used for a militia, its used to protect personal property and justify arms sales to the populace. Although in many ways its not an unreasonable part of the constitution - and even if guns were banned your lone nutter would still find a way; the idea of the 2nd ammendment is to keep the government in check through fear of revolution, rather than a system where the populace lives in fear of the government.
