“The Newsroom” begins its truncated, six-episode final season on HBO on Sunday, and its pilgrim’s progress through 21st-century American journalism has brought it to the Boston Marathon bombings. This gives Aaron Sorkin, the writer of record on every episode, plenty of opportunities for finger-wagging as his fictional ACN cable news crew watches less meticulous or fortunate outlets falsely naming suspects and bannering photos of innocent people.

The First Amendment warriors of ACN are last to the story because of their leaders’ old-school reluctance to use Twitter as a source. In part, this looks like a statement of principle from Mr. Sorkin. The new season, three episodes of which were sent to critics, intensifies his general critique of social media as a tool for gathering and distributing news, with page clicks driving news judgment. (He hedges his bets by having his protagonist, the “News Night” anchor Will McAvoy, appear sympathetic to the new ways.)

But the journalists’ hesitation also makes sense dramatically, because they’re still feeling the effects of their colossal blunder in Season 2, when they broadcast a false report accusing the American military of using sarin gas. It was a mistake for them and for “The Newsroom” — the show stopped making sense late in Season 2, when the whole news crew offered to resign but no one ended up leaving. The show doesn’t have to be scrupulously realistic about the news business, but some things — like falsely accusing the Marines and then not firing anyone — are harder to overlook than others.

Season 3 begins with both ACN and Mr. Sorkin in a tamped-down, focused mode. That’s generally a good thing. Some unhealthy story lines have been cauterized — in particular, the junior producer Maggie Jordan (Alison Pill) has apparently gotten over the trauma of her deadly assignment in Africa.