The Heller case hinges on whether a state or D.C. can prohibit firearm ownership. In short, regulate it. If a state can prohibit ownership, then it can also protect ownership. So instead of seceding, why not just pass laws protecting handgun ownership or amend your state constitution to protect it? Duh!
The natural order of government is to prohibit tools of freedom. Leaving the issue of prohibition/protection up to the legislature is to subject a natural right to the whims of those who would rather you not have it. The whole point of a “bill of rights” is to pointedly tell the government “hands off - it’s not yours to control in either direction”.