Back in reality, most people who commit mass murder do so because they were brainwashed and incited to do it on message boards. There's not much distinction between a soldier acting on orders and a guy on Stormfront trying to impress his comrades. And it's pretty obvious and easy, if you have a platform like say the Rwandan government radio station, to put out messages that encourage people to kill each other. And kill each other they will.
Does that mean that each individual who killed someone isn't personally responsible? Hell no. They're responsible. But someone who puts out the call to kill people and expects - yes, knows for sure - that one in 100,000 of their followers will pick up the gun, is equally responsible.
I bet when you see an Israeli settler kill a Palestinian kid, you hold the Israeli government accountable. I bet when you see a white cop shoot a black kid in the US, you hold the police responsible. I bet when you heard the Jews were murdered in the gas chambers, or all the Sioux died of smallpox, you didn't hold the individual soldiers accountable: You blamed the government that sent them to do the dirty deed.
Governments have free speech, just like corporations and just like individuals. But except for very rare cases where an individual is executed under law by the government, it's always an individual who kills another individual. Yet no killer gets his ideas in a vacuum.
Most people are too weak to resist the call to dehumanize others. That call to dehumanize and kill is usually sent by groups - religious groups, political groups, or in the modern day Facebook groups. To claim that the airwaves are free and no one holds responsibility except the individual who did the killing is like saying that individual Nazis acted alone to kill Jews. It is absurd on its face.
Just look at the situation on the ground. There is a vast mass of people who will murder each other in every country if they feel they have sanction from the powers higher up. (There's a whole wildly popular movie series about this in the US called "The Purge" which is popular because it appeals to this impulse).
For any moderator or company-moderator, or radio station or other controller of the flow of information to permit and profit from the overabundance of dissemination of calls for genocide, is to be complicit in genocide. Whether or not they pull the trigger, they are responsible for manipulating popular thinking. The mob does not operate on the morality of the individual; and manipulating the mob is the job of governments and corporations. One cannot wash their hands after simply standing on a platform 400 ft in the air and saying that someone should die and then that person miraculously being killed.
The people who pull the trigger may have a harder time living with themselves, when they realize they were just pawns. But it's the people who give them the sanction who are equally, if not ultimately responsible.
Do not confer onto the rest of the human race the values you think you would uphold under the circumstances you imagine, where you might act on your conscience to save lives contrarily to the way everyone around you was acting. That's not how things have ever worked in real life.