On Wednesday Facebook unveiled its long-anticipated program for media companies to publish their stories directly to its platform, rather than on their own sites. Called “Instant Article,” it is available first on the iPhone. In the U.S., The New York Times, BuzzFeed, NBC News, The Atlantic, and National Geographic are participating. Four additional international publications have joined the alpha test. Facebook chose these partners for leadership in their respective categories—a newspaper, a social news outlet, a broadcast station, a magazine known for its long-form journalism, and a magazine known for its striking photography.

Media circles have anticipated this move since last fall and had plenty of time to pontificate on it before it even became official. (The leaks have been many. This is a media-industry story, after all.) Their reaction: Equal parts caution, excitement, fear, and resignation.

Facebook FB offers the new publishers faster loading times for stories viewed within the Facebook app than if they were taken to the publisher’s website. The publishers are given use of Facebook’s media tools, which allow users to zoom in on photos or tilt their phone to move through a series of them.

One notion driving Facebook’s effort is that most publishers make lousy technology companies. Their websites and mobile applications aren’t as slick and mobile-friendly as Facebook’s. With this deal, Facebook argues, publishers have an opportunity to change that—and make money on the deal by pocketing revenue from any ads they sell around their content. If Facebook sells ads around their content, it splits the revenue with the publisher. To the media industry, all of this is exciting.

And frightening. Media companies fear the possibility of a single company like Facebook controlling so much of the digital distribution channel. For example, Facebook bans photos of genitals and nipples on its service, though it permits breasts if they are “actively breastfeeding” or showing “post-mastectomy scarring.” It has changed its policy on beheading videos from banned to permissible, so long as the clips raise awareness rather than celebrate violence. It has censored content on behalf of governments, particularly in Turkey, India or Pakistan.

Anyone worried about censorship could simply choose not to publish on Facebook or opt to find banned content elsewhere. But the concern grows louder each time the small handful of large, powerful Internet companies move to own a bigger piece of the digital world.

Facebook is especially powerful. With 1.4 billion monthly active users, the company now drives a quarter of all Web traffic, which is enough to make or break some publishers. It accounts for one of every five minutes Americans spend on their smartphones. More than half of millennials say they get news from Facebook each day. That dynamic becomes more direct after some of the most trusted media organizations in the world begin using Facebook as their publisher.

As I wrote in March, every time Facebook changes the algorithm of its News Feed, it sends a ripple effect over the media landscape. From the outside, it appears that Facebook has the power to elevate publishers and app makers that it likes and destroy the ones that it does not.

But the company insists it is a benevolent ruler of the Web. At the Code/Media conference in Laguna Niguel, Calif. in February, Facebook chief product officer Chris Cox moved to assuage those fears: “We don’t want to try and devour and suck in the Internet.”