If people had called one another to prepare this, would we say that the phone was responsible for the attack? And would we try to ban phones?
That's a moot point, because an attack like this can't realistically be organized via one-to-one communication. It needs a broadcast medium, which the phone network isn't.
Yeah, of course. Broadcasting means one-to-many communication. Before modern technology, those things were organized using other kinds of one-to-many communication, such as in-person meetings, rallies, and through newspapers and other kinds of publications.
Movements aren't organized one-to-one like on a telephone, because that's a far slower way of spreading a message. It's also an unreliable medium, as the children's game "telephone" shows.
And pretty bad at doing it. It's actually pretty funny to imagine someone trying to organize a movement via a phone tree.
The upside of broadcasting is that issues that only minorities experience have been brought to daylight: #metoo, gay marriage, actual insurrections that we should support, demonstrations, health care fight in the US, etc.
Whether they have the ability to moderate or not is irrelevant. If you can't afford the obligations of a publisher, don't be a publisher.
Regarding moderation, it's true that you can't moderate billions of people with 100% accuracy, but you can discourage them from posting undesirable content in the first place by associating real consequences such a a permanent ban (or a monetary loss, by charging an entry fee to create an account) or make them earn the privilege of posting content (for example, not being able to post links until your account has certain reputation of good behavior).
Discouraging people from posting bad content, and not amplifying the reach of bad content for engagement's sake should go a long way.
Instead, these people were groomed over a period of months or years by way of recommending conspiratorial or outrageous content and it finally blew up.
So not only did Facebook create the problem in the first place, they also had plenty of early warnings about what's been going on, but it's hard to consider an increase in "engagement" (thus revenue) as a "warning" and even harder to act upon it.
This also raises another question regarding the efficiency of our intelligence services if large-scale domestic terrorism was organized all in public on a platform they had privileged access to.
This is free expression, they are providing a platform as free as you going in the street and expressing yourself.
If the government wants to censor this type of expression, it must pass laws, and it must dictates what you can say or can't say. With such a move, social medias would become forbidden, or inefficient (as every post would need to be approved before being released).
If this is the world you want to live in, it's fine, but you need to understand the consequences and the ways to get there.
The street does not automatically reshape itself to promote the most offensive graffiti to as many people as possible.
I wouldn't have a problem with Facebook being hands-off if it was limited to content you explicitly followed in reverse-chronological order (like it used to be), as all you'd need to filter out the bullshit is to not follow bullshit sources. Of course, Facebook's revenue would drop off a cliff if they made this change because bullshit is what drives Facebook's revenue and not the friends/family pictures users originally came there for.
The phone network is useful for other uses society deems to be net-negative, such as spammy calls. As a result, technical and legal barriers were erected to curtail such abuses.
I would have no problem banning certain phone numbers that only exist to incite violence.
Social media is new, and it provides communication fan-out unlike anything we've dealt with before except from people that are powerful enough to be given a platform on major TV networks.
Guns don't kill people, but...
AFAIK, postal service is a public service, but not phones.