As for whether police officers are bound by duty to protect & serve, the answer is both yes and no. They are required to enforce the law and apprehend suspects, and by these actions they do indeed protect & serve, as their cars commonly advertise as a sign of goodwill. They are not, however, required to directly, physically defend citizens from harm (most officers would, I'd expect, but it is not required), and for the most part (with the more dire, critical cases) this is moot anyway because they almost always won't be there while the harm is being done; this is not their fault because there is no practical way for them to be present when they (and their guns) would be needed the most. This is a good basis for the argument that citizens potentially have the same defensive needs as police officers. The odds may be different because the latter must sometimes seek confrontation in the line of duty, but the needs for the worst-case scenarios are the same. This is supposing that a debate even reaches this point, which it should not because of what I said earlier--it's not about justifying a need on our part.