And it’s one of the best things that ever happened in human history.
Would it have come across as less of a threat if he had quoted JFK ("Those who make peaceful revolution impossible will make violent revolution inevitable")? Was JFK threatening Latin America when he said that to their diplomats?
It applies on the small scale as easily as the grand. If you insult someone's mother, watch for and avoid the retaliatory punch. If you violate the privacy of a billion people, call them morons for trusting you, profit greatly from their personal information, and continue to demonstrate eroding ethics, then install a safe room in your house(s) and hire some bodyguards.
That said, individual violence is reasonable, after the non-violent and collectively-violent possibilities have been exhausted. There always has to be some way to effectively retaliate against anti-social behavior.
Rich people get kidnapped and held for ransom to fund rebellions or criminal cartels. It's a thing that happens. Even heads of state get assassinated from time to time. It's a thing that happens. At the level of super-rich that Zuckerberg inhabits, I'd guess he already gets at least 2 attempts at theft, robbery, blackmail, or extortion per year, and some of them might even be successful. It's a thing that happens. People don't like to talk about it, because the successes encourage further attempts.
There were even GTA 5 missions entirely about manipulating public stock prices by criminally compromising or killing a company's CEO. That's how the player can make all three of their player-characters multi-billionaires.
I'm simply saying that if the only way someone can get to you is via criminality, then that is the way someone will get to you. Most people would always try the "legitimate", peaceful option first, if there is one. That's the primary reason why people choose to leave themselves open to the law. Surrendering to the marshals or getting arrested by state professionals is a more favorable alternative than getting caught by an angry mob. Just ask Qaddafi.
It's just engineering. If your structure is designed to fail at one weak point, then you can monitor that possibility more carefully, and predict the behavior following that particular failure. You can purposefully put in a weak element, so that if the structure collapses at all, it will do so more slowly and in a safer direction. In a corporate structure, you allow yourself to be removed by majority vote, and the failure mode is that you get paid off and live on in semi-retirement. Remove that option, and you don't know how you'll leave your office. It might be a memento-mori-scale heart attack, or complete failure of the company, or a sudden black screen as "Don't Stop Believing" plays on the jukebox.
In the wake of the vote to remove him, Zuckerberg could either step down voluntarily, or increase his security. He won't do the former, so he should do the latter.