What people are concerned about are the newsfeeds and timelines, specifically. Companies like Facebook and Twitter and YouTube love to pretend that their newsfeed/timeline products are just like chat apps or phone calls--neutral messaging platforms.
They're not. And the specific reason they are not, is the algorithmic timeline and content suggestions.
It's silly to worry about giving these products "the power to determine what people can—and can’t—say online." They've already seized it for themselves--by deciding for me which content will show up in my newsfeed/timeline/suggested list. They decide which content gets promoted to me.
Yes they use an algorithm to do so, instead of human decisions. But guess who built the algorithm?
Companies that run algorithmic newsfeeds and timelines need to own their role as a publisher and a gatekeeper of content.
Instead of pretending they don't make choices, they should be introspective and thoughtful about the criteria they are using to make those choices. "Engagement" is not neutral criteria because emotions are not symmetrical. Engagement is higher on topics of fear, anger, rage, violence. That's down to our evolution; that's down to the amygdala.
So if you build a publishing system designed solely to maximize engagement, it's going to become a system that preferentially serves content that feeds negative emotions. There are articles and case studies where a person starts with a fresh account and sees what kind of content gets pushed to them; inevitably they get horrible conspiracy theories and fear-oriented content.
Making decisions about what content your audience sees is an act of publishing, even if it's executed via complex algorithm. The companies doing this need to accept their responsibility for what they decide to serve and promote.