Once again, this is all about the fact that the Second Amendment does not exist in a vaccuum: It exists within reality, and reality is that your your rights are bracketed by the need to avoid violating my rights.
Are terrorists criminals? Were the planes destroyed on 9/11 weapons? Would some "martyr" infected with smallpox be considered a weapon? Would Saddam, bin Laden or Arafat be considered a criminal based on their actions?
Once again, this is all about the fact that the Second Amendment does not exist in a vaccuum: It exists within reality, and reality is that your your rights are bracketed by the need to avoid violating my rights.
Unless I USE a WMD against you, I have not in any way violated your rights. For the sake of argument consider a hypothetical - that animals have rights as well (not debating one way or another, just an example). Assume you have somehow become lost in the wilderness. At night, you build a fire (a potential weapon) to PREVENT attacks by creatures of the night. YOU have not violated any rights - they certainly don't have the right to attack you - that violates your rights. So even though you possess the weapon, and use it wisely, the balance is still equal.
If your fire managed to get out of hand and destroy thousands of acres and destroy wildlife, then you have violated the "rights" of others. You're a bad dude, and should be made to pay for your crimes.
So even though I might possess a WMD, it's not until I deploy the weapon improperly (assuming like fire or a plane that it has other uses), or deployed at all (a nuke) that I infringe upon your rights. The mere possession of that same weapon in no way infringed upon your rights.