But, I don't think that e.g. the guerrillas of Vietnam were morally ambiguous simply because they engaged in asymmetric warfare against the US military. They were fighting against identified soldiers in a declared war; they had the right to engage by the international rules / norms of war. They killed people who had taken up arms against them. (Yes, most of their opponents were forced to take up arms; that doesn't make the opposing force morally ambiguous in its opposition.)

They're very different from various terrorists (domestic and foreign) who have attacked the US in recent years, who also reached the conclusion that only asymmetric warfare would work against the US, but chose to attack non-combatants - office workers, children, etc. And they weren't merely casualties of a morally-ambiguous operation; they were direct targets. (As it happens, these terrorists were not particularly effective, either.)

So even if we want to grant modern interpretation to the Second Amendment and read in the right to do whatever is effective against the government of the US (instead of talking about what it was crafted to do), it still seems to me like it should be about making sure you have the arms and the training to defend yourself against an illegitimate government and establish your own, perhaps through asymmetric warfare if needed - which is still very different from randomly attacking individual officials whom you have declared corrupt in an otherwise-legitimate government (let alone their family members).