For example, I would never blacklist Breitbart, because I'm not interested in censoring political opinions I disagree with. I just want to free us from the burden of these websites that add nothing to the world and leech attention from everyone.
The slope is very slippery. It is very easy to put forth an argument that some left/right wing media "[adds] nothing to the world and [leeches] attention from everyone"
Keeping the focus on blatant spam sites is a noble cause, but this tool is as easily misused as a firearm.
Let me be more precise, and use tptacek's words in https://news.ycombinator.com/item?id=12999887: "fake news = spam sites built from scripts consisting largely of a backcatalog nonsense stories [...] with a one or two carefully produced fake stories as a "payload".
I think this definition is as objective as it gets, and clearly excludes things I might disagree with politically, but are not the target of this extension.
I think the reverse assumption - that everything should be considered a valid information source until conclusively proved otherwise - is probably a more dangerous bias than assuming that some media does add nothing to the world.