Inexplicably, the two series are under assault again. In December, PBS’s flagship station, WNET (Channel 13) in New York, proposed bumping the series from Monday and shifting them to the same time slot on its much smaller sibling station, WLIW (Channel 21). The two programs would be broadcast on WNET as reruns — nearly a week later, at 11 p.m. on Sundays. WNET wants to devote Monday night to arts programming, a driver of financial support for member stations; its decision could prompt PBS to shift the two series away from the prime-time schedule across much of the country. Amid a new outcry, PBS and WNET have put off a decision until May.

This is much more than a scheduling change; it could devastate independent documentary filmmaking. WLIW has about half the viewership of WNET, and does not reach some core parts of the New York region. Moving the films out of prime time means fewer reviews, and less publicity. It also threatens funding: When filmmakers apply for grants from foundations or philanthropies, the promise of a robust distribution platform is crucial. The proposal also sends the signal that nonfiction films on challenging subjects are less important to PBS and WNET than costume dramas.

“Independent Lens” and “POV” take on critical social issues overlooked by commercial outlets. They leverage the power of television to expand freedom of expression for people whose voices are not easily heard in American media. Freedom of expression is hollow if you can’t be seen or heard.

The two series also provide an outlet for minority filmmakers. A 2014 study by the Center for Media and Social Impact at American University found that “Independent Lens” was much more diverse than cable: over 80 percent of the documentaries had at least one minority character, and 30 percent of them had at least one minority director — compared with 13 percent for documentaries on HBO and zero at CNN and ESPN. These two series attract among the largest audience of black viewers of any PBS program.

At town-hall-style meetings in San Francisco, New York and Chicago, filmmakers and their supporters have called on PBS and WNET to go back to their roots: serving diverse audiences and expanding the national dialogue on critical social issues. The controversy has also been debated at the Sundance Film Festival and South by Southwest.