It's easy to verify that a plugin modifies the Facebook site and block links to it. It's much harder to tell whether the list of fake news sites it uses is itself fake or the plugin is a security issue, let alone whether particular articles are truthful.

> It's easy to verify that a plugin modifies the Facebook site

No, it doesn't. That's a serious abuse of the language. What you describe would be hacking into Facebook.

What the plugin does is help me not load content I don't want.

The browser is my user-agent and I'm instructing it how to display the content delivered to me.

> It's much harder to tell whether the list of fake news sites it uses is itself fake

Exactly, and yet they're trying harder to block a fact checker than to block the bad news.

If they just backed off on both I could see the bad news and have my plugin flag it.

> or the plugin is a security issue,

Not even close. It's not like Facebook is cleaning up malware plugins.

They're only targeting this one because it threatens their editorial control of my feed.

which they are completely within their rights to do

Well, actually, perhaps not. That's the point. Past a certain size, if you're sleazy and manipulative we're going to control your actions.

But even if, how is that "sure, but you can't legally stop them" a defense? How is it one you feel compelled to make?

Especially because I can technologically stop them. They can block one plugin, and detect one set of blocks, but it's a game we've played many times before and the defense always loses.