Not Facebook

Per FiveThirtyEight:

But the analysis also showed that these same people were often involved in ideological communities — communities built online and offline, where future terrorists sought (and often found) support and validation for their ideas. Thirty-four percent had recently joined a movement or organization centered around their extremist ideologies. Forty-eight percent were interacting in-person with extremist activists and 35 percent were doing the same online. In 68 percent of the cases, there’s evidence the “lone wolf” was consuming literature and propaganda produced by other people that helped to shore up their beliefs.

More than half the time, someone knew about the terrorist’s plan before it was carried out. (A fact that also turns up in research on school shootings in the United States.)

There’s been very little empirical research on lone actor terrorists. But what does exist has been enough to convince some researchers that “lone wolf” is a moniker that never should have existed. The ties to communities of extremist thought and social pressure are too strong to ever say someone was truly acting alone.

No one “acts alone”. Carrying out a hateful action alone doesn’t wash away all of the motivation which led the person to taking that action in the first place. The inspiration for an attacker is rooted in ideas from other people, and other communities which help inspire that hatred.