Rachel Joseph / Submitted photo via TNSCaroline (Sarah Lancashire) and Alan (Derek Jacobi) hug in the hospital as Celia (Anne Reid) stands next to them in “Last Tango in Halifax.” The show, which recently began its third season, is one in a string of scripted dramas produced by PBS.

PASADENA, Calif. — Quality drama — or at least TV shows with an aspiration to be quality drama — rules the TV, cable and online streaming worlds.

Whether it’s “Halt and Catch Fire” on AMC or “Kingdom” on DirecTV’s Audience Network or “American Crime” on ABC or “House of Cards” on Netflix, all programmers aspire to put on shows with a patina of serious, realistic quality.

So it’s understandable that PBS, riding the success of “Downton Abbey” on “Masterpiece,” would want to up its drama game, too. And there’s no reason to begrudge PBS’s efforts but it does derail one line of defense of PBS’s existence.

Prior to the success of “Downton,” PBS’s “Masterpiece” was pretty much the only source of original drama on PBS. (PBS stations sometimes picked up British imports but those were bought by the local stations; they did not come from PBS.)

Once “Downton” hit and raised PBS’s profile among younger viewers, PBS started airing scripted dramas on Sunday night outside the “Masterpiece” banner, including “Call the Midwife” and the now-canceled “Bletchley Circle.” PBS even added a scripted comedy, British import “Vicious,” back for its second season Aug. 23.

Last month, PBS debuted the third season of “Last Tango in Halifax” and a one-season drama, “The Crimson Field,” which has already been canceled in England.

In January, PBS announced its first American scripted drama in about a decade, the six-hour “Mercy Street” (formerly known as “Mansion House”), set at a Civil War hospital and filmed this spring in Richmond, Virginia. “Mercy Street” is expected to air its episodes on Sundays in January concurrent with the final season of “Downton.”

At a January press conference, PBS president Paula Kerger said there are no plans to expand PBS’s drama footprint beyond Sunday night.

“Some of our stations are airing drama also on Thursday nights,” Kerger said. “But the problem with being a variety service is that we’ve created a destination for science on Wednesdays, history on Tuesday nights, our collective experience on Mondays with ‘Antiques Roadshow,’ ‘Genealogy Roadshow’ and (independent film). So figuring out a really good place for additional drama is something that we wrestle with. Right now, we’re very focused on Sunday nights.”

Kerger said because of the success of “Downton,” “Masterpiece” now has underwriting as does “Mercy Street.”

“That gives us flexibility to add into the schedule,” she said. “We’re not doing more drama at the expense of other things.”

Because it receives taxpayer funding, PBS always seems to be under scrutiny with some calling for its dismantling. One of the defenses of PBS is that it offers programming that can’t be found elsewhere. Bravo and A&E abandoned the arts years ago, leaving PBS the only TV outlet (aside from tiny cable network Ovation) to give the fine arts any attention. With true science programming in short supply on cable, PBS offers serious science shows other outlets do not.

But with drama, PBS is jumping on the same original scripted series bandwagon that’s being chased by seemingly every cable network, no matter how small.

“It seems not that long ago we were all lamenting about the lack of great scripted drama, and here we are awash in really great stories,” Kerger said in January, adding that PBS has a unique role in telling a history-based story. “We do really great history documentaries, and we really try to put our collective experience in perspective. I think for a lot of people, the best way to bring them into those stories is through drama. So we’re not looking to do drama just for drama’s sake. We are looking to do drama that we feel is a little different from what everyone else is doing and that very much ties into our goal, which is not just to entertain, but also to educate and inspire.”

Kerger said PBS’s longtime relationship to the Civil War, through Ken Burns’ landmark documentary, made “Mercy Street” a natural fit.

“We saw with ‘Downton’ that some people watch drama that may not come to a historical documentary and the drama gets them thinking about the historical time frame,” Kerger said after the press conference. “We’re doing drama as a backdoor way to really tap into history.”