The legitimacy of an act (violence in this case) is highly subjective. The legality is a lot more objective. In this particular scenario, I think I would rather say that the government has a legal monopoly on violence. The legitimacy argument breaks down for oppressive governments where some revolting citizens take up violence because they see it as their last and only option. Some might argue that their act is legitimate, but it is still illegal. Now, one could always say that if the violence by government is not legitimate, it is no longer a government. But that is largely a philosophical/literary point. Here, when people are saying that Government has a monopoly on violence, they mean that the voters have granted them a legal right to do use force (which is at least pseudo-aggressive if not violent in all cases). The legitimacy can be contested in courts and debated upon in the next election - but till then, they reserve the monopoly.
> The legitimacy of an act (violence in this case) is highly subjective.
In the sense Weber uses it, it may be fuzzy, but its not subjective (its essentially the aggregate of how it is treated by the people in the territory.)
> The legitimacy of an act (violence in this case) is highly subjective.
The idea that legality is objective in a way legitimacy is not is debatable.
> I think I would rather say that the government has a legal monopoly on violence.
Perhaps, but that seems to be a trivial tautology, in that what is legal is precisely, by definition, what is formally allowed by some government.
> The legitimacy argument breaks down for oppressive governments where some revolting citizens take up violence because they see it as their last and only option.
Weber would state that, to the extent that this is a general failure over some subset of its territory, the entity has failed as the government of that territory -- that, in the case where no entity exercise a legal monopoly on violence over a territory, there is no government, and in the case where there is such an entity but its not the one that is claiming to be the government, then the claiming entity is simply wrong.
> Some might argue that their act is legitimate, but it is still illegal.
In the eyes of the purported government that they are revolting against, but not in the eyes of the purported government that they have formed in the revolution. Legality has no meaning without reference to a governing authority.
