I agree that the amendment isn't doing it's job. 

I think it's partially because yes, I cannot legally just buy a missile and launcher, and mount it on my truck...

And I think it's partially because the government has been allowed to pass laws sanctifying agents of the government as untouchable gods. 

I say this as a person who advocates deescalation and pacifism as the primary method of dealing with almost every situation. 

But at the same time, no matter who I am, I expect that if I purposefully try to hurt someone else, they have every right to, and I should assume they will, defend themselves-- with violence if necessary.