If there is a section of the nation which the state does not have legal hegemony over (either due to gang control or other factors), it is the state's moral obligation to remove any competing centers of power, by force if necessary.
Sometimes but not always
I think the moral obligation and moral right belongs to the government that will offer the greatest freedom to the people who live in the disputed region.
For example, if a totalitarian regime seeks to regain control of a rebel area that trying to establish a democracy, the moral right belongs to the rebels.
Was listening to a political commentator and thought this was an interesting claim.
I voted disagree because it depends on the nature and degree of the control.
Take certain parts of Central America, wherein there are locations in which cartels are the chief center of power: yes. It is the obligation of the state to regain control of its territory.
However, the statement is far too broad, and agreeing with it would be to completely justify the occurrences at the colony in Waco, which I don't entirely agree with.
Then again, to maintain a freedom-oriented democracy, one must be able to enforce the ability of others to maintain their freedoms, and if one has a case in which the state is not the chief center of power, that cannot be effectively done.
I suppose this is a difficult question for me.
You have stated it well, though I would omit the word “moral.”